Each provider's available hours are subject to a number of configuration options. For every day of the week that the practice is open, a time range (from and to) specifies the provider's availability. Within that range, a number of breaks can be set up for each day of the week. And if some day doesn't follow the usual schedule, you can always specify alternative hours for just that day, if any, producing one-time "overrides" for holidays, vacations and other one-offs.
In combination, these configuration options offer a powerful way of managing provider's availability. Even then, practice staff can still schedule appointments in violation of provider's configured hours, but patients will never be able to do so.