If they insist you take a shower or you need to take a shower, you have very little time to actually fuck. The upside is they dont have to haul ass to get to the next appt if back to back, so you probably wont be rushed out like you would at the end of the hour.
True story - I once was doing a session with one of my favs. She insisted on getting me off second time even though we were going close to OT and apparently she had a client next. After I CIMd, she rushed me really quick to the shower, she didnt shower herself, just spit out and took some mouthwash while putting on her clothes. I took the quickest 3 minute shower in my life and hopped out. Hastily put my clothes on, exited the room and heard footsteps right behind me and then knock on the door.