On June 16th we plan to visit Hanauma Bay, Diamond Head, and Pearl Harbor. I know that it is important to arrive at Pearl Harbor early and also Hanauma Bay is best in the a.m. Any suggestions on what order to do these three things in one day?

All three are great in my opinion but probably not possible in one day (if you plan on swimming/snorkeling). I suggest Pearl Harbor then H. Bay.

I'll suggest the opposite. Get to Hanauma Bay as soon as it opens, which is I think around 7am. By 9am it will start to get crowded, you can go hike Diamond Head before the heat of noontime. Go to Pearl Harbor after that. You might have to wait, but you can do all three in one day.

Because I'm such a resourceful gal, (and interested in visiting Hanauma Bay myself in a few weeks), I checked the hours for you. The Hanauma opens at 6am. The last program at Pearl Harbor begins at 3pm, and it is first come, first served. If you get there by 1pm, I'd bet you'd get in. Good luck!

Before you finalize your itinerary, check whether Pearl Harbor is open. They were scheduled to close for 2 weeks in June for repairs, but there have been reports that the closing has been delayed.

Actually, all of the activities that you mentioned are best in the early morning. If you can't make it to DH by 9:00am, I would suggest waiting until later in the afternoon or it will be a long hot hike.

Several weeks ago we hiked to the top of Diamond Head and then thought we would cool off at Hanauma Bay. By the time we got to Hanauma it was full and we had to do Hanauma another day.

Hanauma Bay typically fills their parking lot before 9 a.m. By 8 a.m. it will already be half full. You can come in by foot later but you'll need to find parking somewhere down the hill.

As suggested, Diamond Head is also a morning activity. It is pleasant early in the morning but once the sun starts to heat the volcanic rock it becomes an oven. I wouldn't want to start up Diamond Head any later than 9:30 a.m.