
**Apache Airflow version**:

master

**What happened**:

https://github.com/apache/airflow/blob/master/airflow/models/baseoperator.py#L356 --> should be timedelta not datetime


tests/serialization/test_dag_serialization.py
#
#
#
"""Unit tests for stringified DAGs."""
import importlib
import importlib.util
import multiprocessing
import os
import unittest
from datetime import datetime, timedelta, timezone
from glob import glob