To leave a gap or buffer between appointments, padding can be added to the Appointment Type by clicking "Block off extra time before or after..."
For example, to leave a 30 minute space between appointments for travel, clean up, prep for next appointment, or a snack/bathroom break, you'll enter 30 minutes after the appointment. See screenshot below:
The Client's Scheduling Page will only show the duration of the appointment to the client, but will block off the duration plus the padding on your calendar. In this example, the appointment would show as a 60-minute appointment, but the total duration of the appointment (including the 30 minutes of padding) is 90 minutes. There must be enough availability for the duration plus padding, otherwise availability will not show on the scheduling page.
Keep in mind -- When you add padding and also sync to an external calendar (Google calendar, Outlook, or iCloud), padding is not included in the synced appointment! We only sync the duration field over, not the padding field.