All industries differ
For example Accountants/ solicitors, there is no waste in their time as in they charge for every minute/ hour etc and charge for preparing for their services aswell.
In your case for your typical meeting you have a period of time getting ready and , cleaning up after etc. Some girls that will be 2 mins before and after but the top girls could be 40 mins between before and after and add another 20 mina for sifting through messages for bookings etc
On thar basis she really has an hour unpaid time per booking.
Using this logic.is why I would be giving.discounts for good regulars booking 3.and more hours.