Hey Brian,
I can I do this by just changing my system clock, or does the TF server program do anything internally that will prevent this?
Changing the clock won't work. The TurboFloat Server will likely detect the tampering and just say "OK, I'm forcing you to check now" or even simply "Not activated".
The best thing you can do to test the behavior is to set days_between="1" and grace="1".
Is there something in particular you need to know?