I'm currently working on a spreadsheet to gather data on the most popular times of day that users are online on a particular piece of software.

Basically I need to create a bell curve of the data, and I'm working with data that covers a whole month.

My data is split into two columns: the date, and the time. It's formatted like this:

A B
1/9/2012 9:15:32

Now I want to classify the times into 30 minute sections (i.e. 8:30am-8:59, 9:00am-9:29 etc etc), to show the curve more clearly. How would I go about putting all that data into the right context to create a bell curve?

Any suggestions would be great as I'm struggling!

Thanks!