I guess that depends on when you are going. If you are going during the summer and it is your intention to hit all the slides, you'll probably find long lines won't get to do much before having to leave for your ADR. I don't know about you or if you have any kids in your group, but water & sun makes us sleepy and the kids cranky. So dinner may be a "scene". My own opinion, but this is just based on our group, I wouldn't schedule an ADR on a waterpark day. It may be hard to get your kids (if you have any) to leave and everyone may be tired. We would just eat back at our room and veg.