docs: def _get_delta(self, now, then):
          """
          Internal helper which will return a ``datetime.timedelta``
          representing the time between ``now`` and ``then``. Assumes
          ``now`` is a ``datetime.date`` or ``datetime.datetime`` later
          than ``then``.
  
          If ``now`` and ``then`` are not of the same type due to one of
          them being a ``datetime.date`` and the other being a
          ``datetime.datetime``, both will be coerced to
          ``datetime.date`` before calculating the delta.
  
          """
          if now.__class__ is not then.__class__:
              now = datetime.date(now.year, now.month, now.day)
              then = datetime.date(then.year, then.month, then.day)
          if now < then:
              raise ValueError("Cannot determine moderation rules because date field is set to a value in the future")
          return now - then