Very normal request, especially if you are going back home to a wife or something. Just make sure your shower time fits inside the paid time. Don't think you get an hour of play, and then a 20 min shower also. If you are good with a quick 5 min shower, then stop playing at the 55 min mark. That is just respectful of the lady and her time.

b-

Five minutes, tops.

Dry off in the tub, don't get the flour all wet.

Hang the towel up to dry.

I sometimes shower before the appointment as well as afterwards.  Yes, the time is part of the paid time.