I. Love. AK. But with that being said, normally we check out mid-afternoon - for we have a toddler and nap times are key. But if he wasn't with us, we would absolutely take our time admiring details, having a drink at the Dawa Bar, etc. I find the atmosphere and entertainment very relaxing and fun.
Our last trip we actually went to AK at 6pm one night bc it was open until 8. It was completely a ghost town, and so, so beautiful! If you haven't seen the tree of life lit up at night, ridden Everest in the dark, or witnessed some of the details of the lands specially lit up - I 125% recommend it! It really was pretty, and my husband had a hay-day taking pictures.
If you did just want to just hit attractions and head out - I'd say you could probably be out by 1 pm if you are at the park by rope drop. Depending on time of yr that is. One more note - if you've never checked out Rafiki's planet watch, I would suggest checking it out quick. Our last trip they had a female lion in the medical station and it was fascinating to watch the procedure. Never know what animal exam you may come upon.