Posted opening is 9 AM, but they do open 30 - 60 minutes earlier so that the first dolphin swim can start shortly after 9 AM. We got there are 8:30 AM, checked in, got our gear, did the walking tour, got our locker, etc. and were on the beach after 9 AM.
We had opted for a 1:50 PM dolphin swim time which actually put us in the water around 2:15 PM or so.