Nicholas,
Do you want this done automatically or do you want the user to enter the class manually via an added field in Timesheet Pop Up?
Note
For best assistance with Customization questions, please post these questions in the Customization section of the forum instead of the How do I... That will have a larger group of Success Managers and Professional Services Engineers that can quickly provide you answers to these type of questions.
Also, For further clarification, we suggest you register for one of our Advanced Q&A webinars (see the link-> http://www.clarizen.com/resources/online-demo.html#second ).These are great resources for free consulting with our Customer Success Managers and visual answers to your questions.
Sincerely,
Boris