Hi Pigget,
It total depends on how popular the excursion is and how full the ship is. Maybe somebody here knows how popular the excursions you are looking at are, but I dont.
I will tell you this; we have never booked an excursion ahead of time. I know many of my fellow DISers jaw just dropped and cant understand how anyone could possibly not die of anxiety with such a detail unplanned weeks before the cruise.
As a matter of fact, since we only book when the Florida resident rates are available, we dont even book the cruise until 4-6 weeks out (did I just hear more jaws dropping?). We always just visit the excursion desk once we get on board and see whats left. So far we havent been disappointed, but after four cruises we may start to need to book in advance just to get excursions we have not done yet.