Right now, we are definitely "early birds." We have two little ones who are up at 6:45-7:00 am every day! Basically, we're twiddling our thumbs waiting for the parks to open! We head back to the hotel around 1-2pm for nap time, and then head back around dinner time. But, even with naps we only make it until about 10. The latest we've ever made it was 11. That was bad, though, because it doesn't matter how late the kids go to bed. They're still up at 7 the next morning, and it meant we had a long (i.e., crabby) day.
When they get older, I assume we'll be more of "late owls." But, personally, I love the parks first thing in the morning. I love pictures with no one else in them, and the feeling that you "own the place." We get a lot accomplished between 9-11 am!