It doesn't take long to check in, 5 minutes or so. If you're not doing the dolphin swim, you don't really need to be there early. You'll obviously have to wait your turn to check in, but since everything else is kind of "do what you want when you want to", being there at 8 or 9 won't make a difference. You'd just have a little less time at breakfast, and more lockers and wetsuits will be taken, but since there's a limited amount of people allowed in a date, it shouldn't be an issue.