I think you want to make sure you are at the airport with time to spare because we have had the security lines be super long OR super short, just depends on how many flights are leaving. One thing I would note though is not much is open at that time in the airport, especially to eat so what we have done in the past is leave Aulani about 3.5 hours ahead of our scheduled night flight and stop just before the airport at a little strip mall called the Moanalua Shopping Centre that has a Panda Express, Ruby Tuesdays, Starbucks, Koa Pancake house, Jack in the Box, Mcds and a Chevron. This is where we gas up the rental car before the return. It is about 6 minutes from the Airport, if that. Just off of the highway on a street called Valkenburgh. That way we have already gotten through any traffic that may have kept us from being on time and we can gauge when to leave for the car rental return.
Thanks for the tip about the gas stop. My plan is to have early dinner at Ulu cafe and leave Aulani around 6:30 PM with the hope to drop-off the car and get to the airport by 8 PM. Hope there won't be traffic in that direction at that time.
Both times we have stayed at Aulani we have requested late check outs on the day of. Both times we were given some time, not a lot but some. First time it was until 1:00 and the second time we were given about an extra hour. Even if this isnt the full day it is a plan to keep in mind.