Buffer time is the gap a business deliberately leaves between one appointment and the next. It is not a break and not a spare slot to sell. It is there for the work that sits around a service: sweeping hair, changing the linen, sterilising tools, writing the client card, taking payment and walking the next client in. Without it, every small delay pushes into the next appointment, and by mid-afternoon the whole day is running twenty minutes late.
In practice
Work it out from the room, not from habit. A massage therapist who needs eight minutes to change linen, wash her hands and write notes, and who books 60-minute sessions back to back, is either cutting the massage short or running late. Adding 10 minutes between sessions turns an eight-session day from 8 hours into 9 hours and 10 minutes. Keeping the 8-hour day instead means seven sessions, because 7 sessions of 60 minutes plus 6 gaps of 10 minutes is exactly 480 minutes. At $100 a session, that buffer costs $100 a day, which is the honest price of not rushing.
Some services need more than others. A colour may need a buffer for the basin and the bowls; a gel removal needs one for the dust. Set a buffer per service where your diary allows it, rather than one blanket figure.
Buffers are also where a late client is absorbed. A ten-minute buffer lets you start someone five minutes late and still finish on time, which is the basis of most late arrival rules. Do not confuse buffer time with processing time, which is time inside a service while the client is still in the chair.