docs: def get_last_update_of_model(self, model, **kwargs):
          """
          Return the last time a given model's items were updated. Returns the
          epoch if the items were never updated.
          """
          qs = self.get_for_model(model)
          if kwargs:
              qs = qs.filter(**kwargs)
          try:
              return qs.order_by('-timestamp')[0].timestamp
          except IndexError:
              return datetime.datetime.fromtimestamp(0)