The full day is the unit at risk. A six-hour session cancelled on Friday afternoon cannot be filled, which is why deposits exist and why their terms have to be recorded rather than remembered.
Artists are independent in practice. Separate diaries, separate rates, separate waiting lists and often separate earnings arrangements: a single studio calendar hides all of it and creates arguments.
Consent forms and aftercare given are a health record. Signed on the day, retained and retrievable, they matter if anything goes wrong and they are checked by inspection.
Deposits are held money, not income. Recording what is held, against which booking and which artist, prevents the month-end confusion that arises when takings and deposits share one figure.