In your Self-Book templates you have two template types that allow visitors to add events to your calendar: "Make a Reservation" and "Suggestion an Event." The “Make a Reservation” template lets visitors suggest a time to book a private event to take place on your Calendar. The “Suggest an Event” template lets visitors suggest a public event onto your Calendar that your other Calendar visitors can see and attend. Both of these template types are added to your calendar instead of your individual events.
Since both of these templates give users flexibility about when they can add events to your calendar, you have the option of turning on a feature that limits how far in the future that visitors can add events to your calendar. You can turn this option on for any of your custom "Make a Reservation" or "Suggest an Event" templates and you can limit bookings anywhere from 1 day to 1 year in your calendar.
To learn how to turn this feature on follow the steps in the image below:
When your visitors try to book ahead of the future limit that you set then they will see a message similar to this one: