To 藍色兔寶寶: Dry Tortugas

Thanks to your suggestions of Dry Tortugas, I'm planning to visit the island after Thanksgiving. One question - did you make advance reservation of the tour boat and how much ahead did you make your reservation? I know I can call the tour operator and I'm sure they'll tell me to reserve now. But I would rather not to have make too much advance reservation in case of last minute change. Many thanks.