The only time I booked the BTFT was when I had FTTF. There were no lines at the excusion desk, yet there were only three spots left for the second tour.
So, I suggest you make a bee line to the excursion desk to sign up. (And YES, it was worth it!)
Last April, on the Dream, I ran into problems with scheduling for Trivia and such at the wrong time. Also, the Dinner menus were missing the entre page every day.
So, keep that paper copy of the Fun Times handy!