It definitely can be a full day experience. Mid day in summer heat, lines for the popular slides can get lengthy increasing time spent. I would schedule at least 5 hours total but plan on a full day.
Heck, just between the wave pool and the lazy river, we've been in the parks for 2-3 hours alone. If your boys are fish and love to swim/be in the water, yep, full day. Don't forget to reapply your sunscreen over and over again!