Adding time in php

Hi All I have two tables with columns of times that it took to perform tasks eg: 8:40 6:50 8:30 10:55 --------- 34:55 total time taken to complete the tasks in hours and minutes I am able to add the times with sql however I need to add the totals to cone up with a grand total and because of the makeup of the tables I cant use sql. I am there for going to have to use php code and this is where the problem comes in because in sql there is SEC_TO_TIME and TIME_TO_SEC functions that allow easy addition of the times but I cant find an equivalent in php. Does any one know of a way that I can add to times together in php.