
**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
ui_fgcolor = '#000'  
    pool = ""  
    
    _base_operator_shallow_copy_attrs: Tuple[str, ...] = (
        'user_defined_macros',
        'user_defined_filters',
        'params',
        '_log',
    )
    
    shallow_copy_attrs: Tuple[str, ...] = ()
    
    operator_extra_links: Iterable['BaseOperatorLink'] = ()
    
    __serialized_fields: Optional[FrozenSet[str]] = None
    _comps = {
        'task_id',
        'dag_id',
        'owner',
        'email',
        'email_on_retry',
        'retry_delay',
        'retry_exponential_backoff',
        'max_retry_delay',
        'start_date',
        'depends_on_past',
        'wait_for_downstream',
        'priority_weight',
        'sla',
        'execution_timeout',