We are a waterpark family! Due to our shorter vacation this time, we'll only be able to hit TL (and not BB) but we plan to be there open to close, 9 am to 8 pm. In fact, we're squeezing HS and AK into one day so we'll be able to devote the whole next day to TL.
We may head over to the MK afterwards in time for Wishes since our resort is close enough, but we think the waterparks are just as important as the other four parks, especially if you have any waterbabies. The last couple of hours at the park are the best, as most people leave mid-afternoon, especially if there's been a summer afternoon rain shower. At that point, you can walk right on most of the rides.
Amusingly, my 14-year old DS will NOT ride thrill rides at all, but he'll do everything at a water park, even those really steep slides I won't do. We tease him that he would probably ride a roller coaster if someone would just sit beside him with a squirt bottle the whole time.