
**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
"Invalid arguments were passed to {c} (task_id: {t}). Invalid "
                    "arguments were:\n**kwargs: {k}".format(c=self.__class__.__name__, k=kwargs, t=task_id),
                )
            warnings.warn(
                'Invalid arguments were passed to {c} (task_id: {t}). '
                'Support for passing such arguments will be dropped in '
                'future. Invalid arguments were:'
                '\n**kwargs: {k}'.format(c=self.__class__.__name__, k=kwargs, t=task_id),
                category=PendingDeprecationWarning,
                stacklevel=3,
            )
        validate_key(task_id)
        self.task_id = task_id
        self.label = task_id
        task_group = task_group or TaskGroupContext.get_current_task_group(dag)
        if task_group:
            self.task_id = task_group.child_id(task_id)
            task_group.add(self)
        self.owner = owner
        self.email = email
        self.email_on_retry = email_on_retry
        self.email_on_failure = email_on_failure
        self.start_date = start_date
        if start_date and not isinstance(start_date, datetime):
            self.log.warning("start_date for %s isn't datetime.datetime", self)
        elif start_date:
            self.start_date = timezone.convert_to_utc(start_date)
        self.end_date = end_date
        if end_date:
            self.end_date = timezone.convert_to_utc(end_date)