def expires(self):
        """Union[datetime.datetime, None]: Datetime at which the table will be
        deleted.

        Raises:
            ValueError: For invalid value types.
        """
        expiration_time = self._properties.get("expirationTime")
        if expiration_time is not None:
            # expiration_time will be in milliseconds.
            return google.cloud._helpers._datetime_from_microseconds(
                1000.0 * float(expiration_time)
            )