Ten minutes in the cage among sharks might be the one experience that you remember most vividly from your Hawaii vacation. There are plenty of companies that offer this service on all islands. You are put underwater in a metal shark cage, and you will be immediately surrounded by these dangerous and beautiful ocean creatures.
In fact, the sharks usually are not aggressive, they are just curious and attracted to the boat. However, it is still a pretty scary adventure. Diving with sharks can be done at any time. However, in summer, it's better because there are fewer waves and the ocean is calmer. If waves are too big, the dive could be canceled for safety reasons.