code: def start_at(self, start_at):
          
  
          if start_at is None:
              raise ValueError("Invalid value for `start_at`, must not be `None`")
          if len(start_at) < 1:
              raise ValueError("Invalid value for `start_at`, length must be greater than or equal to `1`")
  
          self._start_at = start_at
docs: Sets the start_at of this Shift.
          RFC 3339; shifted to location timezone + offset. Precision up to the minute is respected; seconds are truncated.
  
          :param start_at: The start_at of this Shift.
          :type: str