you could do this all in your query.
the sql function for subtracting two times is TIMEDIFF, for adding two times ADDTIME
heres an example query using real time values:
SELECT TIMEDIFF('2010-12-24 12:13:44','2010-12-24 04:15:44') as time1, TIMEDIFF('2010-12-22 11:13:44','2010-12-22 02:15:44') as time2, TIMEDIFF('2010-12-20 9:13:44','2010-12-20 5:15:44') as time3, ADDTIME(TIMEDIFF('2010-12-24 12:13:44','2010-12-24 04:15:44') ,ADDTIME(TIMEDIFF('2010-12-22 11:13:44','2010-12-22 02:15:44'), TIMEDIFF('2010-12-20 9:13:44','2010-12-20 5:15:44'))) AS totalHours;
or to use the columns in your DB:
SELECT TIMEDIFF(Out1, In1) as time1, TIMEDIFF(Out2, In2) as time2, TIMEDIFF(Out3, In3) as time3, TIMEADD(TIMEDIFF(Out1, In1) ,TIMEADD(TIMEDIFF(Out2, In2), TIMEDIFF(Out3, In3))) AS totalHours