We were just at Aquatica this past week. There are actually 2 different options for All Day Dining.
The first option is the one FLOIR described above, allowing you to eat from any of the 3 dining locations in the park. The price, per person, is $34.99 for that plan.
You can also get an all day dining pass for just the Banana Beach Buffet. You are not restricted to once per hour, you can come and go as often as you like (just flash your dining wrist band as you enter) and all food must be eaten within the restaurant perimeter (no taking food out with you). The all day pass for the Banana Beach Buffet is $24.99. In comparison, a one-time visit to Banana Beach is $14.99.