I still dont think this is correct. Your booking system allows reservations to be booked back to back not giving any offset when done in the way I mention.
I think the simple fix to this great booking system is to add the offset to any reservation.
EG. A 1 hour treatment with an offset of 30mins would become 1hour 30 mins. If a customer trys to book a similar treatment in the previous hour they would get the warning message and asked to choose a different / earlier time.
