This is configured per service and adds a 'Preparation' block slot before every booking:

You can omit it during manual booking by unticking Book in preparation time:

Within Settings > My Business, click the pencil (edit) icon against the staff members service and update preparation time within advanced settings:

This is configured per staff member and adds an 'Additional Time' block slot after every booking:

You can omit it during manual booking by unticking Book in additional time:

Within Settings > My Business, click the pencil (edit) icon against the staff members and update Block additional time after every booking:

This can be used for services like hair colouring where there is some downtime in the middle that you can potentially free up for another appointment.

Within Settings > My Business, click the pencil (edit) icon against the barber/therapist's service and update appointment pattern within advanced settings:

Suppose the service length is 75 minutes and the barber/therapist's timetable spacing is 15 minutes, in the example above, the service comprises 5 x 15-minute slots (0-15, 15-30, 30-45, 45-60, 60-75). If the 30-45 slot is marked red as available, a booking at 11:00, for example, will have a gap between 11:30-11:45 for a 15-minute appointment:

TIP: If you want to replicate services from one staff member to another, use the [Copy to another barber/therapist] button: