Excel 2007 : How to categorise into hours.

Hi team,

I have start and end times and i've been asked to categorise them by hour e.g.
if the task started at 5:30pm and ended at 8pm, then it would like this

5-5:59pm - 30mins
6-6:59pm - 60mins
7-7:59pm - 60mins

A sample spread sheet is attached for your reference.

Cheers,
Krishna.