The format is in 'HH:MM:SS' or HHMMSS format, depending on whether the function is used in a string or numeric context.
mysql> mysql> SELECT UTC_TIME(), UTC_TIME() + 0; +------------+----------------+ | UTC_TIME() | UTC_TIME() + 0 | +------------+----------------+ | 02:46:23 | 24623.000000 | +------------+----------------+ 1 row in set (0.00 sec) mysql>