When I do outcalls I will propose to shower together at the beginning, especially because I often arrive via bus/metro and I want to be extra fresh, despite always showering right before leaving my place. I think this feels more appreciated to offer to shower together since I'm doing so during the time, but some folks are okay letting me shower alone at the start so in those cases I'll just try to hurry up a little more. At the end, I always like to shower alone and I still consider it part of the time for an outcall, and this usually takes me about 10 minutes.
If I'm hosting an incall, I gently ask that they shower upon arrival, and if they invite me to join them in the shower I will do so even though I'm already fresh, assuming the date started from the incall (I like to arrive in advance to shower before my date shows up). For incalls, I usually only hop in the shower after the person has left so it's technically not part of the total time. If everything is going perfectly, I can get all of my cleanup done within about 20 minutes. I strip the bed, throw everything in the wash and start the machine, then jump in the shower. Once I'm out of the shower I tidy up the place, change the sheets, and right before leaving, if I timed it all right, the washing machine is done and I can stick the load in the dryer and start the cycle on my way out the door.