My wife and I went on this whale watching tour on August 27. We opted for the morning tour. My understanding is that you have about as good a chance to see anything whether you go morning or afternoon. We saw a lone hammerhead shark (though I only really saw the dorsal fin). The coolest part was the megapod of dolphins -- they said possibly up to 1,400 dolphins. Unfortunately, no whales! But it was fun to get out on a boat ride. My wife found a Groupon that got us just under half the regular price. Had we paid full price (almost $50/ea) and not seen any whales, I'd have been more disappointed. (Yes, I understand the guides can't control where the whales are.)
I would recommend this, and hopefully you get lucky enough to see a whale.