Teaching Elapsed Time

I need to teach a basic understanding of elapsed time to my fourth-graders. 

While there are many excellent center-type games, what I'm really looking for is word problems or activities I can put on the interactive whiteboard.

Here's an example of something my kids would have trouble with:
Kyle started his homework at 4:05 p.m.  He has football practice at 5:45.  How long does he have to complete his homework before he has to go to football practice?

Do you have any good word problems, web sites, or whiteboard activities to help with this?

Thanks in advance for your help!