That seems a little long to me too. Maybe if you were going to one of the moderates or Pop and you also had to walk across the resort when you got back, then it could be an hour and a half.
The boat line isn't usually as long, but the monorail also takes a lot of folks at one time, and January (Except right near New year's ) isn't a peak time. When you walk up to that are, you can see how extensive the crowds are for each form of transportation. I'd also encourage you to watch Wishes from Main St - and leave right away.
Keep in mind, they also want you to arrive before your ADR time. I'm also assuming that you are NOT talking about the luau show, which only seats at certain times.
If you do get there early, it is pretty easy to kill a little time at the Poly - esp. after a day inthe park. Check in, then tour the art gallery. After that, grab a seat and relax in the lounge area.
Last, it is possible to see the fireworks from 'Ohana - I think it is. I've never done it from there, but I understand they pipe in the Wishes music during the show. If that's the case, you'll want an ADR for an hour before the start of the show.