Generally speaking, it is almost always best to snorkel in the mornings through most of Hawaii. That is because the winds often start to pick up in the afternoon (or earlier), which brings waves.
Also the parking lot can fill up at Hapuna, so it is better to go earlier.
As we mentioned on our page here about Hapuna Beach, be careful of currents.
Have fun snorkeling Hapuna, it is a beautiful beach.
