You should try to plan on getting to USS Arizona first thing and then most likely it will take a solid 4 hours +/-, depending on how detailed you are being, including boat trip out to memorial. Nice view of Diamond Head from Outrigger also.

I agree with the others that there is lots to do on Oahu, the Arlington of the Pacific (Punch Bowl), Pali Lookout, North Shore, hike up Diamond Head and a ton of other stuff but unless you are planning on a car you best stick to your plan.

The volcano hike looks cool, we did sunrise at the volcano but had to leave around 2:00AM for the 3 hour drive to the top of the volcano viewing area with sunrise around 5:30 or so. Incredible view and incredibly cold.
Best contact the tour service for the times though, most of it will no doubt be travel to/from.

We spent 10 land based days with 3 on Oahu, 2 Molakai, 4 Maui (or something like that).