When a client is scheduling an appointment, they're shown a list of available times to choose. Ideally, the appointment start times will automatically adjust to each schedule, making sure there aren't time gaps between appointments.
The new Automatic Appointment Start Times setting helps by adjusting the starting times to the shortest service duration available for the selected location and schedule.
For example, if your business has two schedules, one with 15-minute services and the other with 30-minute and 60-minute services, then the available appointment start times listed for the client will be every 15 or 30 minutes based on the selected service and schedule. This will avoid having unfillable gaps on the calendar.
Where: Settings > Appointment Scheduling Policies