Sets the expiration time of @key to @_time
            @_time: absolute Unix timestamp (seconds since January 1, 1970)

def expire_at(self, key, _time):
        """ Sets the expiration time of @key to @_time
            @_time: absolute Unix timestamp (seconds since January 1, 1970)
        """
        return self._client.expireat(self.get_key(key), round(_time))