My unit is having an APFT next month, starting then, you fail 2 tests and they initiate the separation paperwork. I'll be one of the graders as my ankle is still healing from the fracture and I know I wouldn't be able to pass because of it. However, I've already started rehabing myself to start regaining strength in my ankle and leg, once the bone is fully healed and I get the blessing from the VA I can start work on speed and endurance.
The way I look at it, minus injuries and illness, you should be able to pass an APFT at any time with no real heads up, maybe a few hours notice, wouldn't want to take one after just eating a heavy meal.
I know if my chain of command sticks to the new guidelines of kicking people out for failing, and I think they will, then I can see maybe two people in my platoon getting the boot, and probably a dozen or so from the other platoons. Having administered the test a few times recently I know there are about that many who simply fail every single time, showing little to no improvement from one test to the next.