So the time is not stored as minutes (data type: number), but in “hours:minutes” format (data type: time or date)? If so you need to convert your “hours:minutes” format to minutes for example:
1:53 → 1*60 + 53 = 113 minutes
You can do this conversion either on the DB side (recommended) or in each separate Business Objects document with a local report formula (cumbersome). Once you have converted your time format into a “pure” number format you should be able to sum it up.
How to convert a date/time format into a number format with Business Objects Reporter: see here
Which DBMS (Oracle, MS SQL server, etc.) are you using?
Andreas 
(BOB member since 2002-06-20)