diff --git a/addons/purchase/controllers/portal.py b/addons/purchase/controllers/portal.py
index 92136935681..600f7b8f751 100644
--- a/addons/purchase/controllers/portal.py
+++ b/addons/purchase/controllers/portal.py
@@ -3,10 +3,11 @@
 
 import base64
 from collections import OrderedDict
+from datetime import datetime
 
 from odoo import http
 from odoo.exceptions import AccessError, MissingError
-from odoo.http import request
+from odoo.http import request, Response
 from odoo.tools import image_process
 from odoo.tools.translate import _
 from odoo.addons.portal.controllers.portal import pager as portal_pager, CustomerPortal
@@ -134,17 +135,22 @@ class CustomerPortal(CustomerPortal):
             return request.redirect('/my')
 
         updated_dates = []
-        try:
-            for id_str, date in kw.items():
-                line = order_sudo.order_line.filtered(lambda l: l.id == int(id_str))
-                if not line:
-                    return request.redirect(order_sudo.get_portal_url())
-                updated_dates.append((line, date))
-        except ValueError:
-            return request.redirect(order_sudo.get_portal_url())
+        for id_str, date_str in kw.items():
+            try:
+                line_id = int(id_str)
+            except ValueError:
+                return request.redirect(order_sudo.get_portal_url())
+            line = order_sudo.order_line.filtered(lambda l: l.id == line_id)
+            if not line:
+                return request.redirect(order_sudo.get_portal_url())
+
+            try:
+                updated_date = line._convert_to_last_minute_of_day(datetime.strptime(date_str, '%Y-%m-%d'))
+            except ValueError:
+                continue
+
+            updated_dates.append((line, updated_date))
 
         if updated_dates:
             order_sudo._update_date_planned_for_lines(updated_dates)
-
-        values = self._purchase_order_get_page_view_values(order_sudo, access_token, **kw)
-        return request.render("purchase.portal_my_purchase_order", values)
+        return Response(status=204)
diff --git a/addons/purchase/models/purchase.py b/addons/purchase/models/purchase.py
index d2a43bea5bd..dc233ce9498 100644
--- a/addons/purchase/models/purchase.py
+++ b/addons/purchase/models/purchase.py
@@ -711,30 +711,39 @@ class PurchaseOrder(models.Model):
                 order.message_post(body="The order receipt has been acknowledged by %s." % order.partner_id.name)
 
     def _update_date_planned_for_lines(self, updated_dates):
-        if updated_dates:
-            note = self._compose_note(updated_dates)
-            self.activity_schedule(
-                'mail.mail_activity_data_warning',
-                summary="Date Updated",
-                note=note,
-                user_id=self.user_id.id
-            )
+        # create or update the activity
+        activity = self.env['mail.activity'].search([
+            ('summary', '=', _('Date Updated')),
+            ('res_model_id', '=', 'purchase.order'),
+            ('res_id', '=', self.id),
+            ('user_id', '=', self.user_id.id)], limit=1)
+        if activity:
+            self._update_update_date_activity(updated_dates, activity)
+        else:
+            self._create_update_date_activity(updated_dates)
 
-            for line, date in updated_dates:
-                line._update_date_planned(date)
-
-    def _compose_note(self, updated_dates):
-        """Helper method for creating log note when user update scheduled date
-        on portal website."""
-        note = _('<p> %s modified receipt dates for the following products:</p>', self.partner_id.name)
+        # update the date on PO line
         for line, date in updated_dates:
-            note += _(
-                '<p> &nbsp; - %(product_name)s from %(date_start)s to %(date_end)s </p>',
-                product_name=line.product_id.display_name,
-                date_start=line.date_planned,
-                date_end=date
-            )
-        return note
+            line._update_date_planned(date)
+
+    def _create_update_date_activity(self, updated_dates):
+        note = _('<p> %s modified receipt dates for the following products:</p>') % self.partner_id.name
+        for line, date in updated_dates:
+            note += _('<p> &nbsp; - %s from %s to %s </p>') % (line.product_id.display_name, line.date_planned.date(), date.date())
+        activity = self.activity_schedule(
+            'mail.mail_activity_data_warning',
+            summary=_("Date Updated"),
+            user_id=self.user_id.id
+        )
+        # add the note after we post the activity because the note can be soon
+        # changed when updating the date of the next PO line. So instead of
+        # sending a mail with incomplete note, we send one with no note.
+        activity.note = note
+        return activity
+
+    def _update_update_date_activity(self, updated_dates, activity):
+        for line, date in updated_dates:
+            activity.note += _('<p> &nbsp; - %s from %s to %s </p>') % (line.product_id.display_name, line.date_planned.date(), date.date())
 
 
 class PurchaseOrderLine(models.Model):
@@ -936,7 +945,7 @@ class PurchaseOrderLine(models.Model):
             date_planned = date_order + relativedelta(days=seller.delay if seller else 0)
         else:
             date_planned = datetime.today() + relativedelta(days=seller.delay if seller else 0)
-        return timezone(self.order_id.user_id.tz or 'UTC').localize(datetime.combine(date_planned.date(), time.max)).astimezone(UTC).replace(tzinfo=None, microsecond=0, second=0)
+        return self._convert_to_last_minute_of_day(date_planned)
 
     @api.depends('product_id', 'date_order')
     def _compute_analytic_id_and_tag_ids(self):
@@ -957,7 +966,7 @@ class PurchaseOrderLine(models.Model):
             return
 
         # Reset date, price and quantity since _onchange_quantity will provide default values
-        self.date_planned = self.order_id.date_planned or timezone(self.order_id.user_id.tz or 'UTC').localize(datetime.combine(datetime.today(), time.max)).astimezone(UTC).replace(tzinfo=None, microsecond=0, second=0)
+        self.date_planned = self.order_id.date_planned or self._convert_to_last_minute_of_day(datetime.today())
         self.price_unit = self.product_qty = 0.0
 
         self._product_id_change()
@@ -1147,5 +1156,11 @@ class PurchaseOrderLine(models.Model):
             'order_id': po.id,
         }
 
+    def _convert_to_last_minute_of_day(self, date):
+        """Return a datetime which is the last minute of the input date(time)
+        according to order user's time zone, convert to UTC time.
+        """
+        return timezone(self.order_id.user_id.tz or 'UTC').localize(datetime.combine(date, time.max)).astimezone(UTC).replace(tzinfo=None, microsecond=0, second=0)
+
     def _update_date_planned(self, updated_date):
         self.date_planned = updated_date
diff --git a/addons/purchase/static/src/js/purchase_datetimepicker.js b/addons/purchase/static/src/js/purchase_datetimepicker.js
index c2aaad196c4..de1be92f6df 100644
--- a/addons/purchase/static/src/js/purchase_datetimepicker.js
+++ b/addons/purchase/static/src/js/purchase_datetimepicker.js
@@ -1,3 +1,6 @@
 $(function () {
     $('input.o-purchase-datetimepicker').datetimepicker();
+    $('input.o-purchase-datetimepicker').on("hide.datetimepicker", function () {
+        $(this).parents('form').submit();
+    });
 })
diff --git a/addons/purchase/tests/test_purchase.py b/addons/purchase/tests/test_purchase.py
index 19734a815fa..b02154520b0 100644
--- a/addons/purchase/tests/test_purchase.py
+++ b/addons/purchase/tests/test_purchase.py
@@ -144,3 +144,41 @@ class TestPurchase(SavepointCase):
         messages_send = po.message_ids - old_messages
         # check no reminder send
         self.assertFalse(messages_send)
+
+    def test_update_date_planned(self):
+        po = Form(self.env['purchase.order'])
+        po.partner_id = self.vendor
+        with po.order_line.new() as po_line:
+            po_line.product_id = self.product_consu
+            po_line.product_qty = 1
+            po_line.price_unit = 100
+            po_line.date_planned = '2020-06-06 00:00:00'
+        with po.order_line.new() as po_line:
+            po_line.product_id = self.product_consu2
+            po_line.product_qty = 10
+            po_line.price_unit = 200
+            po_line.date_planned = '2020-06-06 00:00:00'
+        po = po.save()
+        po.button_confirm()
+
+        # update first line
+        po._update_date_planned_for_lines([(po.order_line[0], fields.Datetime.today())])
+        self.assertEqual(po.order_line[0].date_planned, fields.Datetime.today())
+        activity = self.env['mail.activity'].search([
+            ('summary', '=', 'Date Updated'),
+            ('res_model_id', '=', 'purchase.order'),
+            ('res_id', '=', po.id),
+        ])
+        self.assertTrue(activity)
+        self.assertEqual(
+            activity.note,
+            '<p> vendor1 modified receipt dates for the following products:</p><p> \xa0 - Product A from 2020-06-06 to %s </p>' % fields.Date.today()
+        )
+
+        # update second line
+        po._update_date_planned_for_lines([(po.order_line[1], fields.Datetime.today())])
+        self.assertEqual(po.order_line[1].date_planned, fields.Datetime.today())
+        self.assertEqual(
+            activity.note,
+            '<p> vendor1 modified receipt dates for the following products:</p><p> \xa0 - Product A from 2020-06-06 to %s </p><p> \xa0 - Product B from 2020-06-06 to %s </p>' % (fields.Date.today(), fields.Date.today())
+        )
diff --git a/addons/purchase/views/portal_templates.xml b/addons/purchase/views/portal_templates.xml
index 0618c182943..5ec71184b6d 100644
--- a/addons/purchase/views/portal_templates.xml
+++ b/addons/purchase/views/portal_templates.xml
@@ -224,10 +224,6 @@
           </div>
         </div>
         <h3 class="font-weight-normal">Pricing</h3>
-
-        <form t-attf-action="/my/purchase/#{order.id}/update?access_token=#{order.access_token}" method="post">
-          <input type="hidden" name="csrf_token" t-att-value="request.csrf_token()"/>
-
           <table class="table table-sm">
             <thead class="bg-100">
               <tr>
@@ -235,7 +231,7 @@
                 <th class="text-right d-none d-sm-table-cell">Unit Price</th>
                 <th class="text-right">Quantity</th>
                 <th class="text-right">Scheduled Date</th>
-                <th class="text-right">Updated Date</th>
+                <th class="text-right" style="color:#3aadaa"><strong>Update Dates Here</strong></th>
                 <th class="text-right">Subtotal</th>
               </tr>
             </thead>
@@ -253,17 +249,20 @@
                     <span t-esc="ol.product_qty"/>
                   </td>
                   <td class="text-right">
-                    <span t-esc="ol.date_planned"/>
+                    <span t-esc="ol.date_planned.date()"/>
                   </td>
                   <td class="text-right">
-                    <div class="container">
-                      <div class="form-group">
-                        <div class="input-group date">
-                            <input type="text" class="form-control datetimepicker-input o-purchase-datetimepicker" t-attf-id="datetimepicker_#{ol.id}" t-att-name="ol.id"
-                              data-toggle="datetimepicker" data-date-format="YYYY-MM-DD HH:mm:ss" t-attf-data-target="#datetimepicker_#{ol.id}"/>
+                    <form t-attf-action="/my/purchase/#{order.id}/update?access_token=#{order.access_token}" method="post">
+                      <input type="hidden" name="csrf_token" t-att-value="request.csrf_token()"/>
+                      <div class="container">
+                        <div class="form-group">
+                          <div class="input-group date">
+                              <input type="text" class="form-control datetimepicker-input o-purchase-datetimepicker" t-attf-id="datetimepicker_#{ol.id}" t-att-name="ol.id"
+                                data-toggle="datetimepicker" data-date-format="YYYY-MM-DD" t-attf-data-target="#datetimepicker_#{ol.id}"/>
+                          </div>
                         </div>
                       </div>
-                    </div>
+                    </form>
                   </td>
                   <td class="text-right">
                     <span t-field="ol.price_subtotal" t-options='{"widget": "monetary", "display_currency": order.currency_id}'/>
@@ -304,8 +303,6 @@
               </table>
             </div>
           </div>
-          <input class="btn btn-primary" type="submit" value="Send Updated Dates"/>
-        </form>
       </div>
     </xpath>
   </template>
diff --git a/addons/purchase_stock/models/purchase.py b/addons/purchase_stock/models/purchase.py
index 56f3a892c10..66c7c136697 100644
--- a/addons/purchase_stock/models/purchase.py
+++ b/addons/purchase_stock/models/purchase.py
@@ -1,6 +1,5 @@
 # -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
-
 from odoo import api, fields, models, SUPERUSER_ID, _
 from odoo.tools.float_utils import float_compare
 from datetime import datetime
@@ -253,24 +252,29 @@ class PurchaseOrder(models.Model):
                     subtype_id=self.env.ref('mail.mt_note').id)
         return True
 
-    def _update_date_planned_for_lines(self, updated_dates):
-        note = self._compose_note(updated_dates)
-
+    def _add_picking_info(self, activity):
+        """Helper method to add picking info to the Date Updated activity when
+        vender updates date_planned of the po lines.
+        """
         validated_picking = self.picking_ids.filtered(lambda p: p.state == 'done')
         if validated_picking:
-            note += _("<p>Those dates couldn’t be modified accordingly on the receipt %s which had already been validated.</p>", validated_picking.name)
+            activity.note += _("<p>Those dates couldn’t be modified accordingly on the receipt %s which had already been validated.</p>") % validated_picking[0].name
+        elif not self.picking_ids:
+            activity.note += _("<p>Corresponding receipt not found.</p>")
         else:
-            note += _("<p>Those dates have been updated accordingly on the receipt %s.</p>", self.picking_ids[0].name)
-            for line, date in updated_dates:
-                date = datetime.strptime(date, '%Y-%m-%d %H:%M:%S')
-                line._update_date_planned(date)
+            activity.note += _("<p>Those dates have been updated accordingly on the receipt %s.</p>") % self.picking_ids[0].name
 
-        self.activity_schedule(
-            'mail.mail_activity_data_warning',
-            summary="Date Updated",
-            note=note,
-            user_id=self.user_id.id or SUPERUSER_ID
-        )
+    def _create_update_date_activity(self, updated_dates):
+        activity = super()._create_update_date_activity(updated_dates)
+        self._add_picking_info(activity)
+
+    def _update_update_date_activity(self, updated_dates, activity):
+        # remove old picking info to update it
+        note_lines = activity.note.split('<p>')
+        note_lines.pop()
+        activity.note = '<p>'.join(note_lines)
+        super()._update_update_date_activity(updated_dates, activity)
+        self._add_picking_info(activity)
 
     @api.model
     def _get_orders_to_remind(self):
diff --git a/addons/purchase_stock/tests/test_purchase_order.py b/addons/purchase_stock/tests/test_purchase_order.py
index 4f9060ba1fd..333a53e8bf6 100644
--- a/addons/purchase_stock/tests/test_purchase_order.py
+++ b/addons/purchase_stock/tests/test_purchase_order.py
@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
-from datetime import datetime
+from datetime import datetime, timedelta
 
 from odoo.tools import DEFAULT_SERVER_DATETIME_FORMAT
 from odoo.addons.account.tests.common import AccountTestCommon
@@ -224,3 +224,37 @@ class TestPurchaseOrder(AccountTestCommon):
         self.po.button_confirm()
         self.assertFalse(self.po.order_line.mapped('move_dest_ids'))
         self.assertEqual(self.po.picking_ids.move_lines[0].propagate_date, warehouse.buy_pull_id.propagate_date)
+
+    def test_update_date_planned(self):
+        po = self.PurchaseOrder.create(self.po_vals)
+        po.button_confirm()
+
+        today = datetime.today().replace(microsecond=0)
+        tomorrow = datetime.today().replace(microsecond=0) + timedelta(days=1)
+        # update first line
+        po._update_date_planned_for_lines([(po.order_line[0], tomorrow)])
+        self.assertEqual(po.order_line[0].date_planned, tomorrow)
+        activity = self.env['mail.activity'].search([
+            ('summary', '=', 'Date Updated'),
+            ('res_model_id', '=', 'purchase.order'),
+            ('res_id', '=', po.id),
+        ])
+        self.assertTrue(activity)
+        self.assertEqual(
+            activity.note,
+            '<p> Wood Corner Partner modified receipt dates for the following products:</p><p> \xa0 - Large Desk from %s to %s </p><p>Those dates have been updated accordingly on the receipt %s.</p>' % (today.date(), tomorrow.date(), po.picking_ids.name)
+        )
+
+        # receive products
+        wiz_act = po.picking_ids.button_validate()
+        wiz = Form(self.env[wiz_act['res_model']].with_context(wiz_act['context'])).save()
+        wiz.process()
+
+        # update second line
+        old_date = po.order_line[1].date_planned
+        po._update_date_planned_for_lines([(po.order_line[1], tomorrow)])
+        self.assertEqual(po.order_line[1].date_planned, old_date)
+        self.assertEqual(
+            activity.note,
+            '<p> Wood Corner Partner modified receipt dates for the following products:</p><p> \xa0 - Large Desk from %s to %s </p><p> \xa0 - Conference Chair from %s to %s </p><p>Those dates couldn’t be modified accordingly on the receipt %s which had already been validated.</p>' % (today.date(), tomorrow.date(), today.date(), tomorrow.date(), po.picking_ids.name)
+        )