When I've used PAM it was not dry in 20 minutes, it usually took several hours - but this was in the summer when the ambient humidity was much higher.
If you're treating for mites your BP shouldn't be on bedding at all. Treat some paper towels with the PAM, allow them to completely dry, and use those as substrate. Keep some pre-treated paper towels on hand so you have dry ones ready to go when your snake makes a mess and you have to replace them.
When using the Reptile Spray my vet recommended spraying it on a paper towel and then wiping the snake with it, rather than spraying the animal. You use less overall, more of what you use ends up on the snake, it's less stressful for the snake (mine hate being sprayed), and you can avoid getting it into the snake's eyes and heat pits. Next time soak the snake, dry the snake, then wipe with the Reptile Spray so it doesn't wash off.