It definitely depends when you go and what you want to do. If you go most days during the fall, winter, or early spring you can do everything in a few hours. I was there a day in January where I was the only non employee I saw for the first half hour to an hour in IoA, it was raining so it kept the early morning crowd away. I did the harry potter Ride, Train both ways, Gringots, Transformers (i.e. Spider-Man 2, same ride), The Mummy twice, sadly no Rip Ride Rockit this time due to the rain, ET, Jurrasic Park, The Wand shop, Dueling Dragons, ate a Mythos, and that was actually taking my time compared to normal and it only took me about 3 and a half hours. In October it was busier, but I did Spider-Man, JP, Mummy, Rip Ride and Rockit, Dueling Dragons, ET, MiB, Dudley Doo Right, Gringots, Train twice, ate in Springfield and shopped in the Seuss area all in about 4 and half hours. To me it's really up to when you go and what your family wants to do, if you like shows it could take at least a day. If you just go for rides you may be able to go on everything in under 8 hours if you have never been there before. If you don't like thrill rides, probably 4 or less. I'm a Uni annual pass holder, but usually only go there to hit my favorites and try whatever is new. Nothing there is must see for me, especially since I realized Spider-Man and Transformers are essentially the same ride and all Gringots is is a 3D version of The Mummy. I enjoy them, but for me it's a get in, do what I want, get out kind of destination.
On the other hand, I've also been there during summer and waited 2+ hours for the Hulk, so...
Hopefully we can be as lucky as you were!!
