
**Apache Airflow version**:

master

**What happened**:

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


airflow/models/baseoperator.py
"""@property: list of tasks directly upstream"""
        return [self.dag.get_task(tid) for tid in self._upstream_task_ids]
    @property
    def upstream_task_ids(self) -> Set[str]:
        """@property: set of ids of tasks directly upstream"""
        return self._upstream_task_ids
    @property
    def downstream_list(self) -> List["BaseOperator"]:
        """@property: list of tasks directly downstream"""
        return [self.dag.get_task(tid) for tid in self._downstream_task_ids]
    @property
    def downstream_task_ids(self) -> Set[str]:
        """@property: set of ids of tasks directly downstream"""
        return self._downstream_task_ids
    @provide_session
    def clear(