Contrary to what Dave says, on a cruise, there is so much activity onboard that you simply can't fit in everything. Breakfast in your cabin, gym- or spa time, maybe a lecture, leisurely lunch, a movie or exercise class or trivia contest, read, or siesta, lecture on digital photography, or a painting class, dinner in a great restaurant, followed by a Las Vegas inspired show and music/dancing until late.
It ain't military, Dave. I've cruised trans-Atlantic twice, and a trans-Pacific, and believe me, boredom is not an issue.
That said, I think cruises are a lousy way to visit port stops. They are NEVER long enough, and 3,000 of your fellow cruisers in port skews the economy. Less to see, and higher prices.
Consequently, I save Hawaii for timeshare stays- at least 2 weeks without breaking it up into more than one island.
Jim