I came and went
The weather early last month wasn't ideal. Rarely over 72 and showery all day. I did alot of snorkeling, but there were high surf advisories almost the whole time so one had to be constantly aware-lest a rip current get you or a surge pushes you into coral. Still I saw alot of great fish, the underwater Olympus camera I bought at the Costco there for $200 paid big dividends.
The only hiking I did was to get to some zip lining and mosquitoes were picking me apart--I don't care where I am at, if I'm being bitten I'm not going to enjoy it much.
As far as road biking goes, from what I saw, I wasn't sorry I didn't bring any gear. Not much shoulder and too much traffic. I was in Princeville most of the time. But I don't think the conditions in the south were great either. Let me know if you road ride and do find something worthwhile. But in short, if I'm going to bike in Hawaii, I'm riding in Kona area north. That's hard to beat.