sum time field in sql .result will get hour,minute & sec format

Question

EarlyLeaveHrs    time(7) --    how to sum time field in sql 

Data

01:18:00.0000000
04:56:00.0000000
00:00:00.0000000
00:15:00.0000000
00:55:00.0000000

reesult will get - 00:00:00 - this format