Thank you Zappo, unfortunately the automatic pause you speak about doesn't actually occur. My app uses the Box2d physics engine and the ad is called in its own function right before a more general 'main loop' (using Repeat...until) of the gameplay. The fullscreen ad is not covering the full screen completely (but like 98%) and doesn't pause. The latter surprised me a bit, because I also read it should pause the whole app.
edit: Actually, I was wrong. The app does pause. The reason I thought it didn't was because I stored the system time for a timer before the ad. Of course it'll count whatever time passed during the ad. The game does pause
I will check using "GetRewardAdRewardedAdMob" a bit more, however I don't want to force users to watch an ad to completion all the time just for the game level to start (unless the reward will be very clear and very optional, like watching a reward ad for an addition life or boost or something, which I am actually considering doing). Still figuring out the least annoying way to do ads effectively, whilst also doing them in ways people are already familiar with in other games.