
**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
"""
        Serialize Operator Links. Store the import path of the OperatorLink and the arguments
        passed to it. Example
        ``[{'airflow.providers.google.cloud.operators.bigquery.BigQueryConsoleLink': {}}]``
        :param operator_extra_links: Operator Link
        :return: Serialized Operator Link
        """
        serialize_operator_extra_links = []
        for operator_extra_link in operator_extra_links:
            op_link_arguments = cattr.unstructure(operator_extra_link)
            if not isinstance(op_link_arguments, dict):
                op_link_arguments = {}
            serialize_operator_extra_links.append(
                {
                    "{}.{}".format(
                        operator_extra_link.__class__.__module__, operator_extra_link.__class__.__name__
                    ): op_link_arguments
                }
            )
        return serialize_operator_extra_links
class SerializedDAG(DAG, BaseSerialization):