You certainly will be able to do everything at least once in one day and the things you really like, you'll be able to do many times. My ds8 and I did the dolphin swim, the lazy river 6 times (its takes half an hour for 1 full circle), the coral reef twice, the stingrays 3 times, have lunch, and still had time to just lay around and play in the swim area and we started packing up around 4:30.
Its not like going to a Disney park where there is no way to see and do everything in one day.
One tip - if the park "officially" opens @ 9:00, arrive around 8:30. This will give you time to check-in, get your guided tour, wetsuits on, lockers, and have some breakfast. You'll be in the park swimming with the fish while everyone is checking in at 9!
HTH,
CDN Prince Charming
P.S. It is pricey but it is absolutely worth every penny! Save the 2nd day for your next trip though.
