Searched quite a bit, think my post is unique.

I have a script that logs each date/time a user has a license activated and when it is deactivated, along with that duration. The output is:

Name Start Finish Duration
Jon 12/16/14 9:00 12/16/14 9:30 00:30
Mark 12/16/14 9:20 12/16/14 9:30 00:10
Tom 12/16/14 9:25 12/16/14 9:45 00:20

I want to determine how many users are using the license at any given time. I've used countifs and sumproduct without success. A graphical output is most appropriate to show usage over a specific date range. I thought that querying a date/time range every minute and counting the number of users on for each minute then output to a graph made sense...just can't figure it out. Thanks for any guidance!