OK, some suggestions, the pineapple plantation has some good pineapple and cinnamon bread and you need to make time for the PCC. A hike up Diamond Head early in the morning is nice as well (we did this the first day we were there and we got up and nothing was open, time change and all).
We were there on Oahu this exact time (today is our anniversary) several years ago. If you have some extra money, I would highly recommend going and spending a couple days on some of the other islands. My favorite so far is Kauai