We just visited TL this past week and discovered a great tip worth sharing ... sleep in and enjoy the waterpark in the afternoon.
We arrived at TL at about 2:00pm on Thursday, it was very crowded. The head count at that time was 5500 people (with a max capacity of about 7500). However, the wave pool and lazy river are always available without a wait. The whole family enjoyed those cooling attractions for the first 90 minutes. At about 3:30pm, the crowd began to dramatically decrease, so we started going on the slides and raft rides with very reasonable 10-15 minute waits. By 4:30pm, there wasn't any tangible wait for anything. We were able to enjoy the place while it was practically empty from 4:30-5:30pm. The kids were all tired by that time, so we headed out (but the park was open until 6pm).