I just went to Typhoon Lagoon for the first time ever over the weekend, and honestly, you can experience everything the park has to offer in roughly 4-5 hours, if you're just planning for a half-day there.
Although, you could very, very easily spend the entire day there. The wave pool is ridiculously fun, and there are some lounging and play areas for the kids. I especially loved the Crush-N-Gusher water-coasters.
However, the Humunga Cowabunga - No thank you. I may as well have let a Clydesdale kick me in the junk than slide down that thing again. That, and the Gangplank Falls 'family raft' were the only things I didn't particularly care for.
While we were there, it was funny that there was a Lilo meet and greet, and Lilo began walking around unaccompanied by one of the 'handlers,' and hardly anyone batted an eye. It was like she was just another person there.
The rest was awesome. In a few weeks we're going back to sample Blizzard Beach.