
**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
):
    r"""
    Set downstream dependencies for all tasks in from_tasks to all tasks in to_tasks.
    .. code-block:: python
        cross_downstream(from_tasks=[t1, t2, t3], to_tasks=[t4, t5, t6])
    is equivalent to::
        t1 ---> t4
           \ /
        t2 -X -> t5
           / \
        t3 ---> t6
    .. code-block:: python
        t1.set_downstream(t4)
        t1.set_downstream(t5)
        t1.set_downstream(t6)
        t2.set_downstream(t4)
        t2.set_downstream(t5)
        t2.set_downstream(t6)
        t3.set_downstream(t4)
        t3.set_downstream(t5)
        t3.set_downstream(t6)
    :param from_tasks: List of tasks to start from.
    :type from_tasks: List[airflow.models.BaseOperator]
    :param to_tasks: List of tasks to set as downstream dependencies.
    :type to_tasks: List[airflow.models.BaseOperator]
    """
    for task in from_tasks:
        task.set_downstream(to_tasks)
@attr.s(auto_attribs=True)
class BaseOperatorLink(metaclass=ABCMeta):