Another person requested and I agree with the idea to make a transition time at the end of an entire appointment, but perhaps a more efficient and flexible way to manage this would be having a toggle that by default adds blocked out time after an appointment with the Title "Covid cleaning" or whatever you want it to be in the options.

It would be taken into account when making booking availability searches and also, once you book the appointment, you can manually delete or edit the blocked out time where applicable. This would keep appointments from being booked too close together when people self book and would also eliminate the problem of transition time adding too much time to appointments when not intended to work that way. (Which leaves you with an untrustworthy schedule and potential large gaps)