Log the elapsed time since another task began:

class CompletedOperator(BaseOperator):
    def __init__(self, other_task_id: str):
        self.other_task_id = other_task_id

    def execute(self, context):
        self.log.info(
            "Process completed succesfully in %s",
            str(
                datetime.now(timezone.utc)
                - context["dag_run"].get_task_instance(self.other_task_id).execution_date
            ),
        )
Process completed successfully in 0:02:10.823002