Let's start with some definitions on this Visits cube:
Slot capacity = the maximum number of visits that can be booked for a specific timeslot for a location
Visit location = a community location where visitors can be received. Every visit location has its own timeslot and capacity settings. Every resident has a visit location assigned.
Schedule = a week definition of visit capacities and timeslots. A schedule can be updated, but the update is not immediately effective (this is only the case when is it newly created).
Book ahead time = how far in the future a visitor can book a visit. During this time, no schedule configuration updates are allowed because these may conflict with existing bookings.
Day capacity = it is possible to update single days within the book ahead timeframe (single days only, not the weekly schedule). This allows making exceptions to the active schedule.
This graph shows the mechanism about the configuration for visits: