Document is Running VERY slowly ... Too many equations to process?

Attached to this post is a copy of an electronic timesheet I have been developing. There are many nuances that go into our organization's schedule resulting in a lot of formulas. I just now began experiencing a sluggish document and have no idea why it is being slow. If you type in a time such as "1500", VBA code automatically converts it to 15:00 (representing 3:00pm). You will notice that there is a significat delay when you type in a time and hit the tab or arrow button to go to the next cell. Any light anyone may shed on this issue is greatly appreciated!