I find the best SP's (and I assume you dear Helena do this as well) will try to leave a full 30 minutes in between appointments. This allows for overtime with a client, early arrivals, most importantly time to shower and clean up and lastly a bit of 'down time' between clients to reset and such. Not to mention time to return calls, texts and manage their next bookings in a timely fashion. Even with half hour breaks between appointments a quality SP should be able to see ample clients per day/week to make a more then comfortable living and with this focus on quality will have repeats as the quality in service is seen by the clients.
SP's who stack their schedule (sometimes back to back to back to back) always run into complications, rushing a good client, no time to manage new calls, we all have been there and countless reviews here show this type of behavior. Even with a well run agency management in place to take care of these tasks the SP's should reserve time between bookings for the reasons mentioned.
Just my thoughts and experiences over the last decade of hobbying.)
Well said !