docs: def send_at(self, value):
          """A unix timestamp specifying when your email should
          be delivered.
  
          :param value: A unix timestamp specifying when your email should
          be delivered.
          :type value: SendAt, int
          """
          if isinstance(value, SendAt):
              if value.personalization is not None:
                  try:
                      personalization = \
                          self._personalizations[value.personalization]
                      has_internal_personalization = True
                  except IndexError:
                      personalization = Personalization()
                      has_internal_personalization = False
                  personalization.send_at = value.send_at
  
                  if not has_internal_personalization:
                      self.add_personalization(
                          personalization, index=value.personalization)
              else:
                  self._send_at = value
          else:
              self._send_at = SendAt(value)