If your hotel is right downtown in Waikiki, just find out the bus number to take and its schedule from your concierage and get it very early in the morning to Pearl Harbor. If you have not, purchase Frommer's Hawaii on $70 a day. That will provide you with lots of get things to do on all of the islands and how you can save a little money and time too. You would want to be at the memorial before it opens; apx. 9 a.m.
Aloha - mahalo