Huck and I went to Ahihi almost directly from the airport—we didn't want to miss a single moment of the sun and
It wasn't a great diving site due to the surge, but we saw plenty of reef fishes.
You can see where we entered from the map: there's a footpath from the parking area to a rocky beach.
(The beach is useless for sunning: it's made entirely of not-so-smooth rocks!)
Be careful when entering the dive site: the water surge is quite strong and the rocks, sharp.
There's only one area, closer to the point, where entrance is via a small-stone beach and not directly off of bigger
I strongly suggest wearing a bootie (not just a fin sock) and donning your fins in deeper water.