My dojo (NOT USAF- though it used to be) counts hours, but if you train 2 hours, you mark down 2 hours towards your test instead of just one. I believe several dojo's do the 1 hour/day thing no matter how much you train though. Even though people can be in the same organization, interpretation from one sensei to another creates a unique dojo environment..... thus the differences in how testing is handled.
In my dojo, we are lucky if testing is held once a year. It just doesn't happen that often, which is fine for me since I hate testing.
It usually seems like he waits until a few people are ready to test for that rank and then it happens. Our last test was held last November for four people taking 5th kyu tests.