Hi there, Justin. I assume you want to set a timer that will run for X seconds, meanwhile you go between artboards, and then whatever artboard you are on it activates when it runs out and goes to "Game Over" or something. Unfortunately, right now Xd isn't capable of doing that. Whatever transitions or timers you have are reset when you change artboards. You can put in a feature request on uservoice though.
If you just use one artboard, and then use component states for the functionality, this is possible, but quite impractical depending on the elements you have there. That's with the limitation that you shouldn't be doing anything in the exact moment the timer activates. Xd can't do 2 interactions at the same time, and if you try to activate another one when the Time runs out, it blocks it.