Sets the expiration time of :prop:key_prefix to @_time
            @_time: absolute Unix timestamp (milliseconds
                since January 1, 1970)

def pexpire_at(self, _time):
        """ Sets the expiration time of :prop:key_prefix to @_time
            @_time: absolute Unix timestamp (milliseconds
                since January 1, 1970)
        """
        return self._client.pexpireat(self.key_prefix, round(_time))