Disney has actually been decreasing their hours the last couple of years, usually the Magic Kingdom. Universal has increased their hours a bit since Harry Potter & Cinemagic. More attendance creates more demand for later park hours. I would wager they will increase their hours again once HP2 opens and attendance spikes. Once Transformers,the new Springfield land, and HP2 opens it will take at least 2-3 days for a tourist to do all the attractions in the parks. Before HP, a lot of tourists were treating each park as half day parks. Of course, if you only do the major attractions, and race through a park without taking time to enjoy the ambiance, you can do any Orlando park, with the exception of Magic Kingdom, in half a day during off seasons.