I am assuming you will have a rental car? I would highly recommend it staying at Aulani and visiting these areas. Assuming this is the case, I think the most important thing when planning is the locations and the logistics. Even though its an island, traffic does not make it quick or easy to get from one end to the other. We found it most time efficient to plan things in similar areas, but also taking the actual activity into account as well.
For example, Diamond Head is near Waikiki. However, Diamond Head is best hiked early in the morning both to avoid crowds, parking hassles, and the hot sun. This is what we did, but we were far too sweaty and gross in our workout clothes to enjoy an afternoon in Waikiki afterwards. If you plan to just spend the afternoon at Waikiki beach, I think you can make it work, but IMO part of the appeal of Waikiki is the shopping and dining and it would be too far to go all the way back to Aulani to freshen up in between. I'd also caution that Waikiki beach itself is underwhelming for any beach time. Its very busy and relatively small - I'd save beach time for Aulani, or plan time on the windward side of the island which has gorgeous beaches. Kualoa Ranch is on the windward side of the island. We spent a morning there, with an afternoon at the beach in Kailua.
IMO, North Shore can be its own day. We started our North Shore day at the Dole Plantation, spent the afternoon in Haleiwa, and also visited Waimea Valley and Laniakea Beach where the sea turtles are. Waimea Valley has a waterfall at the end of it where you can swim; however, I will caution that admission to the trail is $16 per person and its more of a paved nature trail for walking than it is a hike. We worked this in because it was best for maximizing our time on our North Shore day, but I know there are better waterfall hikes to be seen.
I would highly recommend trying to obtain Pearl Harbor tickets in advance (60 days prior) so you know what time your Arizona tour will be, which will allow you to plan this day. Otherwise, you'll need to arrive early in the morning and whatever tour time you're assigned (they are assigned first come first serve) will dictate the rest of your day. We did an organized tour to Pearl Harbor and had a 9:15am Arizona tour time and we were done by 11:30am. I think if you can secure a morning tour time, you could easily spend the afternoon in Waikiki from here. If you don't get a morning tour time, I think the latest tour is around 3pm because Pearl Harbor closes at 5pm. You may hit some traffic, but you could still spend the evening in Waikiki for dinner, shopping, strolling. Things are open a bit later there, and you'd be after all the rush hour traffic heading back to Aulani.
Lastly, for snorkeling, Hanauma Bay is often recommended which is south of Waikiki. This is another location that's best done early in the morning because of parking and capacity challenges. However, I believe there are some people here who have gone later afternoon that found that time to work well too -
@cgattis , was that you? If afternoon can work at Hanauma Bay, this might be a good option after a Diamond Head hike.
My rough itinerary suggestion would be:
Day 1 - Diamond Head / Hanauma Bay (snorkeling)
Day 2 - North Shore / Waimea Valley (waterfall)
Day 3 - Pearl Harbor / Waikiki
Day 4 - Kualoa Ranch / Kailua beach
Since you have a 5th day to work with, you could easily break up Diamond Head/Hanauma Bay, or Pearl Harbor/Waikiki. If you're interested in the Mississippi, you'll need more time at Pearl Harbor anyhow. When planning, keep in mind that you'll be traveling with the flow of rush hour traffic coming from and going to Aulani. I believe the general timeframe is 6am-10am and 3-7pm. Its best to avoid those times, but there were instances when we couldn't, so we managed expectations and built in time to allow for that.