The thing is, snake mites cannot live for more than about two weeks w/o feeding. So they must feed "on the snakes" in this time period. Mites that don't feed will die. That means you only have to spray inside the tank, where the snake is - twice (once for adult mites and once for the hatching eggs).
Also, I believe mites can lay eggs on the snakes. If you start with a clean tank, clean bedding, and clean furnishings, and there's a hatch, the only place eggs could be is on the snake. BTW, I disinfect my tank and furnishings by soaking them in water with bleach for 15 min.
Now, if mites hatch in a tank that's been treated with PAM, they die as soon as they are born and don't live long enough to breed again 
With Provent a Mite you don't have to spray outside the cage. Any mite outside will starve, so why waste the extra spray. Any mite going into the cage will be killed by the PAM.
If using PAM, don't overdo it. One or two seconds spraying above the tank is enough to kill all adult mites. Overkill wastes resources, plus may make the bedding toxic to the snakes, especially if they are replaced too quickly. I usually wait overnight. Good luck.
TC