Hey all - planning a first time trip to Hawaii for my wife and I. I am thinking that we will hit 2 islands. Big Island (staying at Hilton Waikoloa on points) for 5 nights, then Oahu for 4-5 nights to see Pearl Harbor etc. Is that a decent amount of time on each? Also considering Maui over Big Island but can always do a separate trip later for that one.

That sounds like a great introduction. You can't go wrong visiting any of the 2 islands over a 10 day trip. In the future, you'll want to visit the ones you skip on this trip as they each have their charm. Enjoy.

Thank you my friend. I plan on return trips to Kauai and Maui. It seems like there are flights that aren't too expensive to either for me. Could do a 5 day trip on Maui at the Grand Wailea once I have the points saved up.

Sounds pretty good. I think if you want to learn more about Hawaiian culture, Big Island > Maui.
I went to Hawaii last year, Oahu specifically, I'd say theres a lot of stuff there that's worth skipping or finding alternatives. I can go into it more if you want

Happy Hawaii. Whatever you miss - it’ll be there next time! :-)

Your allocation of nights looks like a nice trip.

I like to recommend visiting two islands on trips of 10 or more days. Three or more islands in one trip crosses my line of how much schlepping and packing/unpacking I want to do. The Big Island is large enough that you could only spend your time on the sunnier Kona/Waikoloa side without going to the Hilo/Volcano side or you can allocate at least a full day or two days and an overnight for the latter.

Something to keep in mind is that HNL has, by far, the most flights to/from the Mainland and also the most operated by widebodies and lie-flats. When flying inter-island, Hawaiian has some limited code-sharing with some of the major carriers but otherwise is stand-alone for a frequent flyer program and interline and checked baggage perspective. Southwest is it's own stand-alone but doesn't charge for checked bags.