
**Apache Airflow version**:

master

**What happened**:

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


airflow/serialization/serialized_objects.py
from airflow.utils.module_loading import import_string
from airflow.utils.task_group import TaskGroup
try:
    
    from kubernetes.client import models as k8s
    from airflow.kubernetes.pod_generator import PodGenerator
    
    HAS_KUBERNETES = True
except ImportError:
    HAS_KUBERNETES = False
if TYPE_CHECKING:
    from airflow.ti_deps.deps.base_ti_dep import BaseTIDep
log = logging.getLogger(__name__)
_OPERATOR_EXTRA_LINKS: Set[str] = {
    "airflow.operators.trigger_dagrun.TriggerDagRunLink",
    "airflow.sensors.external_task.ExternalTaskSensorLink",
    
    "airflow.operators.dagrun_operator.TriggerDagRunLink",
    "airflow.sensors.external_task_sensor.ExternalTaskSensorLink",
}
@cache
def get_operator_extra_links():
    """
    Returns operator extra links - both the ones that are built in and the ones that come from
    the providers.
    :return: set of extra links
    """
    _OPERATOR_EXTRA_LINKS.update(ProvidersManager().extra_links_class_names)
    return _OPERATOR_EXTRA_LINKS
class BaseSerialization: