diff --git a/orchestrator/activities/mongo_db.py b/orchestrator/activities/mongo_db.py
index 0bf2649..51606fa 100644
--- a/orchestrator/activities/mongo_db.py
+++ b/orchestrator/activities/mongo_db.py
@@ -453,7 +453,7 @@ class MongoDB(SientiaMonitoring):
                 - metadata (dict[str, Any]): Workflow execution metadata
                 - collection_name (str): Name of the MongoDB collection
                 - last_data_timestamp (str | None): Last processed timestamp
-                  (ISO-format string) for filtering
+                  (formatted per ``DATETIME_FORMAT_MS_WITH_TZ``) for filtering
                 - base_data_filter (dict[str, Any]): Base query filter conditions
 
         Returns:
@@ -475,12 +475,15 @@ class MongoDB(SientiaMonitoring):
             else:
                 # ``notification_queue.timestamp`` is stored as a native BSON
                 # ``Date`` (``Notification.timestamp`` is a ``datetime``).
-                # ``last_data_timestamp`` arrives here as an ISO-format string
-                # (round-tripped through Redis), so it must be parsed back to
-                # ``datetime`` for the ``$gt`` comparison to be type-correct.
+                # ``last_data_timestamp`` arrives here as a string formatted per
+                # ``DATETIME_FORMAT_MS_WITH_TZ`` (round-tripped through Redis),
+                # so it must be parsed back to ``datetime`` for the ``$gt``
+                # comparison to be type-correct.
                 data_filter = {
                     **base_data_filter,
-                    'timestamp': {'$gt': datetime.fromisoformat(last_data_timestamp)},
+                    'timestamp': {
+                        '$gt': datetime.strptime(last_data_timestamp, DATETIME_FORMAT_MS_WITH_TZ)
+                    },
                 }
 
             self.debug(f'Data filter: {data_filter}', metadata=metadata)
diff --git a/orchestrator/activities/slot_manager.py b/orchestrator/activities/slot_manager.py
index 6a6192b..e0f778a 100644
--- a/orchestrator/activities/slot_manager.py
+++ b/orchestrator/activities/slot_manager.py
@@ -337,8 +337,9 @@ class SlotManager(SientiaMonitoring):
 
         # ``timestamp`` is a native ``datetime``/``Timestamp`` (BSON Date from
         # Mongo), which the Redis repository's plain ``json.dumps`` cannot
-        # serialize. Store it as an ISO-format string instead.
-        last_data_timestamp = last_data_timestamp.isoformat()
+        # serialize. Store it as a string formatted per
+        # ``DATETIME_FORMAT_MS_WITH_TZ`` instead.
+        last_data_timestamp = last_data_timestamp.strftime(DATETIME_FORMAT_MS_WITH_TZ)
 
         try:
             self.redis_repository.set(key, last_data_timestamp, ttl=60 * 60 * 5)
diff --git a/tests/orchestrator/activities/test_mongo_db.py b/tests/orchestrator/activities/test_mongo_db.py
index 4e55f12..927f860 100644
--- a/tests/orchestrator/activities/test_mongo_db.py
+++ b/tests/orchestrator/activities/test_mongo_db.py
@@ -504,7 +504,7 @@ def test_load_latest_data_not_none_last_data_timestamp(mongo_db):
         {
             'metadata': {'workflow_name': 'test_pipeline', 'schedule_name': 'test_schedule'},
             'collection_name': 'test_collection',
-            'last_data_timestamp': '2023-01-01T12:00:00+00:00',
+            'last_data_timestamp': '2023-01-01 12:00:00.000000+0000',
             'base_data_filter': {'level': 'ERROR'},
         }
     )
@@ -561,7 +561,7 @@ def test_load_latest_data_run_boundary_no_skip_or_duplicate(mongo_db):
         {
             'metadata': {'workflow_name': 'test_pipeline', 'schedule_name': 'test_schedule'},
             'collection_name': 'test_collection',
-            'last_data_timestamp': boundary_timestamp.isoformat(),
+            'last_data_timestamp': boundary_timestamp.strftime(DATETIME_FORMAT_MS_WITH_TZ),
             'base_data_filter': {'level': 'ERROR'},
         }
     )
@@ -578,7 +578,7 @@ def test_load_latest_data_error(mongo_db):
             {
                 'metadata': {'workflow_name': 'test_pipeline', 'schedule_name': 'test_schedule'},
                 'collection_name': 'test_collection',
-                'last_data_timestamp': '2023-01-01T12:00:00+00:00',
+                'last_data_timestamp': '2023-01-01 12:00:00.000000+0000',
                 'base_data_filter': {'level': 'ERROR'},
             }
         )
diff --git a/tests/orchestrator/activities/test_slot_manager.py b/tests/orchestrator/activities/test_slot_manager.py
index b16c41f..12873ca 100644
--- a/tests/orchestrator/activities/test_slot_manager.py
+++ b/tests/orchestrator/activities/test_slot_manager.py
@@ -297,10 +297,10 @@ def test_put_last_data_timestamp_not_empty_dataframe(slot_manager):
 
     result = slot_manager.put_last_data_timestamp(test_data)
 
-    assert result == '2023-01-01T12:00:01+00:00'
+    assert result == '2023-01-01 12:00:01.000000+0000'
 
     slot_manager.redis_repository.set.assert_called_once_with(
-        'notification_last_timestamp:test_mail_type', '2023-01-01T12:00:01+00:00', ttl=18000
+        'notification_last_timestamp:test_mail_type', '2023-01-01 12:00:01.000000+0000', ttl=18000
     )