Signing up for a Premium Membership is a donation to help Inside Universal maintain costs and offers an ad-free experience on the forum. Learn more about it here.
Show schedules do not come out that early. It is nearly impossible to predict. Show schedules are based upon estimated guest numbers for the park compared to years past and change daily. I can imagine Waterworld will be running shows in 1hr 10min intervals. Look for the actual park operating hours for that day and expect the show to run throughout the day.
from my experience they usually match the last shows with the closing of the park. The show lasts around 15-20 min so hopefully that helps with your estimation. however I myself would avoid the last shows of the day as the exit gates are backed up from the crowds leaving the park. after waiting in all the lines its a bit of a pain to realize you even have to wait in line to exit the park.