Oh, I forgot to answer one of your questions. Yes, most people view AK as a park that only takes about a 1/2 day to catch all the major attractions.
So, many times you will see swarms of people leaving the park by 3 p.m.
Since it is your first trip though, I can imagine you could stay till dusk. Just remember to go on a cool day. The air temperatures inside AK seem at least 10 degrees hotter than any other park due to the lush landscape.