There are only a few things that you may be able to/want to pre-book and shows are not one of them. Premium Dining (Palo), Spa Services, Onboard activities such as alcohol tastings, Royal Gathering phot op, Royal Tea and port adventures pretty much sums up the things to book in advance...
For Disney, they offer 2 showtimes every night, opposite each of the dining times. If you have early dining, you go to the late show (around 8:30pm), late dining--you go to the early show (6:30?). Doors open 30 minutes before the show. I'd get there that early for Tangled, and at least 15 minutes early for the other shows.
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