
**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
"""
        Verify that all example DAGs work with DAG Serialization by
        checking fields between Serialized Dags & non-Serialized Dags
        """
        fields_to_check = dag.get_serialized_fields() - {
            
            'timezone',
            
            'default_args',
            "_task_group",
        }
        for field in fields_to_check:
            assert getattr(serialized_dag, field) == getattr(
                dag, field
            ), f'{dag.dag_id}.{field} does not match'
        if dag.default_args:
            for k, v in dag.default_args.items():
                if callable(v):
                    
                    assert k in serialized_dag.default_args
                else:
                    assert (
                        v == serialized_dag.default_args[k]
                    ), f'{dag.dag_id}.default_args[{k}] does not match'
        assert serialized_dag.timezone.name == dag.timezone.name
        for task_id in dag.task_ids:
            self.validate_deserialized_task(serialized_dag.get_task(task_id), dag.get_task(task_id))