Time computation

I'm trying to total up times. Example: Cell A1, I type in my start time for person x. In cell A2, I type in person x's ending time. In cell A3, I have it set up to calculate the amount of time person x worked that day (h:mm). I do the same for persons y and z in rows B & C. Now...here's where I'm stuck: in cell D3, I want to sum up the times in cells A3:C3 however, if the total happens to be 25 hours and 1 minute, it returns 1:01. (it gets to 24 hours then rolls over to 0 and startes again) What I want to see is 25:01 How can I get this to happen?

Any help is greatly appreciated...

Rob