Advance notice refers to your reservation preferences. In my reservation preferences, I set it to a day (24hr) advance notice, so Advance notice covers the days (visually on the calendar) that are not available for a guest to book. For instance: It is now the 14th and the Advance notice tag covers today and tomorrow, showing me that a guest cannot book today or tomorrow, and that at this moment, they can only book for the 16th or after...because of my reservation preferences. If you have set your reservation preferences to two days, you will note, Advance Notice will reflect that setting on your calendar by covering today, tomorrow and the next day.