This has come up a few times before, someone has now opened a PR that makes this a global+per-dag setting: https://github.com/apache/airflow/pull/5787 and it also includes docs that I think does a good job of illustrating the two modes.
Does anyone object to this being merged? If no one says anything by midday on Tuesday I will take that as assent and will merge it. The docs from the PR included below. Thanks, Ash Scheduled Time vs Execution Time '''''''''''''''''''''''''''''''' A DAG with a ``schedule_interval`` will execute once per interval. By default, the execution of a DAG will occur at the **end** of the schedule interval. A few examples: - A DAG with ``schedule_interval='@hourly'``: The DAG run that processes 2019-08-16 17:00 will start running just after 2019-08-16 17:59:59, i.e. once that hour is over. - A DAG with ``schedule_interval='@daily'``: The DAG run that processes 2019-08-16 will start running shortly after 2019-08-17 00:00. The reasoning behind this execution vs scheduling behaviour is that data for the interval to be processed won't be fully available until the interval has elapsed. In cases where you wish the DAG to be executed at the **start** of the interval, specify ``schedule_at_interval_end=False``, either in ``airflow.cfg``, or on a per-DAG basis.
