"Time intervals determine when appointments can be booked. With hourly time intervals, appointments can only be booked at full hours, e.g. at 10 AM or 11 AM. With 15-minute intervals, they can be booked every 15 minutes, e.g. at 10:15 AM or at 10:30 AM.
To configure your time intervals, open your profile navigation, click on Settings and then on Booking Settings."