diff --git a/app/dao/notifications_dao.py b/app/dao/notifications_dao.py
index 1a6e1ad3d..d142fb595 100644
--- a/app/dao/notifications_dao.py
+++ b/app/dao/notifications_dao.py
@@ -311,11 +311,9 @@ def delete_notifications_older_than_retention_by_type(notification_type, qry_lim
 
         day_to_delete_backwards_from = get_london_midnight_in_utc(
             convert_utc_to_bst(datetime.utcnow()).date()) - timedelta(days=f.days_of_retention)
-        delete_count_per_call = 1
-        while delete_count_per_call > 0:
-            delete_count_per_call = _move_notifications_to_notification_history(
-                notification_type, f.service_id, day_to_delete_backwards_from, qry_limit)
-            deleted += delete_count_per_call
+
+        deleted += _move_notifications_to_notification_history(
+            notification_type, f.service_id, day_to_delete_backwards_from, qry_limit)
 
     current_app.logger.info(
         'Deleting {} notifications for services without flexible data retention'.format(notification_type))
@@ -399,23 +397,15 @@ def _move_notifications_to_notification_history(notification_type, service_id, d
         _delete_letters_from_s3(
             notification_type, service_id, day_to_delete_backwards_from, qry_limit
         )
-
-    stop = -1  # exclusive, we want to include 0
-    step = -1
-    for hour_delta in range(23, stop, step):
-        # We find the timestamp we want to delete all notifications backwards from
-        # We then start 23 hours ago, and do an insert notification history before deleting all notifications older
-        # We then look 22 hours ago, do an insert notifications history before deleting all notifications older
-        # We continue this until we reach the original timestamp we wanted to delete notifications backwardsfrom
-        # This enables us to break this into smaller database queries
-        timestamp_to_delete_backwards_from = day_to_delete_backwards_from - timedelta(hours=hour_delta)
-
-        deleted += insert_notification_history_delete_notifications(
+    delete_count_per_call = 1
+    while delete_count_per_call > 0:
+        delete_count_per_call = insert_notification_history_delete_notifications(
             notification_type=notification_type,
             service_id=service_id,
-            timestamp_to_delete_backwards_from=timestamp_to_delete_backwards_from,
+            timestamp_to_delete_backwards_from=day_to_delete_backwards_from,
             qry_limit=qry_limit
         )
+        deleted += delete_count_per_call
 
     # Deleting test Notifications, test notifications are not persisted to NotificationHistory
     Notification.query.filter(
diff --git a/tests/app/dao/notification_dao/test_notification_dao_delete_notifications.py b/tests/app/dao/notification_dao/test_notification_dao_delete_notifications.py
index 78e559e96..88a517a1a 100644
--- a/tests/app/dao/notification_dao/test_notification_dao_delete_notifications.py
+++ b/tests/app/dao/notification_dao/test_notification_dao_delete_notifications.py
@@ -222,10 +222,14 @@ def test_delete_notifications_does_try_to_delete_from_s3_when_letter_has_not_bee
     mock_get_s3.assert_not_called()
 
 
+@freeze_time('2020-03-25 00:01')
 def test_delete_notifications_calls_subquery_multiple_times(sample_template):
-    create_notification(template=sample_template, created_at=datetime.now() - timedelta(days=8), status='delivered')
-    create_notification(template=sample_template, created_at=datetime.now() - timedelta(days=8), status='delivered')
-    create_notification(template=sample_template, created_at=datetime.now() - timedelta(days=8), status='delivered')
+    create_notification(template=sample_template, created_at=datetime.now() - timedelta(days=7, minutes=3),
+                        status='delivered')
+    create_notification(template=sample_template, created_at=datetime.now() - timedelta(days=7, minutes=3),
+                        status='delivered')
+    create_notification(template=sample_template, created_at=datetime.now() - timedelta(days=7, minutes=3),
+                        status='delivered')
 
     assert Notification.query.count() == 3
     delete_notifications_older_than_retention_by_type('sms', qry_limit=1)