If you have two time values, and you want to know the time difference between them, you can use the TIMEDIFF(time1, time2) function as shown below:

SELECT TIMEDIFF(TIME('19:26:50'), TIME('09:26:50'))

FROM DUAL;

10:00:00

SELECT TIMEDIFF('1997-03-01 19:26:50.000123',

'1997-02-28 09:26:50.000000') FROM DUAL;

34:00:00.000123