Excel 2007 : Tracking minutes over hours of the day.

Any help would be appreciated.

I have some tasks completed throughout the day, and i'm trying to figure out how to see which hours are busiest. I've hit a few snags. One, if the task started at, say, 3:10PM, and ended at 4:30, I would like to see 50 minutes under 3o'clock hour, and 30 minutes under the 4o'clock hour, etc. Second, sometimes they run over midnight. Thanks.