Are you speaking for this July? If so, I'd start pricing it out and booking asap. Prices will only go up from here as they sell more. And once they're sold out, they're sold out. So I would suggest doing it as soon as possible.
You might get lucky, but seeing as how July is considered a busy season, the day before, the dolphin swims may very well be sold out. You could probably get a reservation to get into the park the day before, but probably not a swim, and it'd be the most expensive the day before, I would assume.