Oracle - RESTAR DOS HORAS

SELECT TO_CHAR(TO_DATE('00:00:00','HH24:MI:SS') +

               (TO_DATE('19:25:00', 'HH24:MI:SS') - TO_DATE('18:00:00', 'HH24:MI:SS')), 'HH24:MI:SS') Diferencia

FROM   SYS.DUAL;