Your services have a set duration that breaks down your hours of availability into appointment timeslots. The time in your availability must be greater than or equal to your service's duration in order for appointment timeslots to display to clients who are booking with you.
For instance, if you are a massage therapist and have a “Deep Tissue Massage” service that lasts for 1 hour (60 minutes) and your Service Availability from Staff Profile is set up between 9:00am – 5:00pm, you could have appointments scheduled from:
Alternatively, if you have a “Hot Stone Massage” service that is set for a duration of 90 minutes (1 hour & 30 minutes), the appointment time offerings would be:
No one would be able to book a 90 minute massage after 4:30pm because your day is set to end at 5:00pm. The thing to realize about setting your service durations is that there has to be enough time left in your availability to account for the entire duration of you last appointment.
Please note: In the example above, all the appointment times displayed based on the full service duration. If I would prefer to have my appointment start times display every 15 minutes for more options for my clients to choose from, I can do that by adjusting my Time Panel Settings (found underneath Settings → Time) which determines how appointment time slots are displayed.