It varies by competition. The most common (for us in our area) is 6 minutes on the stunt mat, 6 on the tumble strip, and six on a full floor (could be dead or spring). We've had competitions where is was 5 minutes per mat, competitions where it was 9 minutes per mat and pretty much every time in between.
Summit it just a full spring floor with 12 minutes, and UCA was the same way when I competed there (I assume it is still the same now).
American Championships actually had 4 mats, I can't remember how much time we had on each though but it felt like we had too much time. It was essentially a stunt mat, another stunt mat, tumble strip, and then a full floor.