Booking duration is how long the booking occupies availability. A 60-minute booking starting at 10:00 normally uses capacity until 11:00.
Booking frequency controls how often a new start time is offered. With a 15-minute frequency, customers may see 10:00, 10:15, 10:30, and 10:45 when capacity allows. Both settings are in the booking list editor under General → Availability and offer values from 15 to 120 minutes.
The frequency does not shorten the booking duration. A start time is offered only when the whole booking fits before the end of the working-hours period, and several bookings can overlap only when the configured capacity supports them.
If services take different amounts of time, enable Services for the list. The duration then shows Based on selected services, and each booking uses the duration of the services chosen. After changing timing settings, test the first and last slots of the day and a period with overlapping bookings.