I've looked through your project, and have some observations ...
Your Screen handling is wasteful of yours and our time. Please see the Screens FAQ at FAQ Section: Screens and read the articles on many screens and why you shouldn't open Screen1.
Retire your rubber stamp.
Your timing considerations can be handled by use of two extra global variables, all within the same screen:
- Start game Instant (Clock1.SystemTime taken at start of session)
- Session milliseconds End Deadline (Clock1.SystemTime plus session time limit (1 year for no limit)
- Level number (for deciding to show the time limit or not)
Does your division problem generator need to be restricted to integer quotients?
P.S. The Project -> pulldown has a Save As option. Time to rename your project. It's not Mole Mash.