Leave an extra two hours more than the driving time, so that you have time to stop a few times along the way. Be flexible with where those might be, since it might be raining, or not have parking, but there are dozens of little waterfall/outlook hikes along the way. Pick two or three, and take it tranquilo.

Check into the hotel there for two nights. Hamoa beach was my favorite on the island. Nice waves, nice sand, not a lot of people.

Really cool hike on the Pipiwai trail that was most of the day once you include a visit to the pools near the coast. Impressive banyan tree, and the highest waterfalls we saw the whole time.

We drove home the opposite way around the drier side of the island. Again, a few waterfall hike stops if you've got time. It's fun to do the full loop. A few bumpy spots in the road. Recommend high clearance.