Booking capacity is the amount of service your location can accept at the same time. A slot is offered only when enough capacity remains for the entire booking duration.
Existing bookings, blocked days, working hours, start intervals, service duration, party size, and applicable floor-plan rules can all affect the result. Two bookings with the same start time may be valid when capacity supports both.
If a customer cannot see an expected time, check the selected service first, then review its duration, the bookings that overlap it, and the list's opening and advance-notice rules.
After changing capacity, test both a small and large booking and inspect the final slot of the day. This catches settings that appear correct in the middle of an empty calendar but fail near a boundary.