code: def get_registration_dt(self, use_cached=True):
          
          device_json = self.get_device_json(use_cached)
          start_date_iso8601 = device_json.get("devRecordStartDate")
          if start_date_iso8601:
              return iso8601_to_dt(start_date_iso8601)
          else:
              return None
docs: Get the datetime of when this device was added to Device Cloud