It is all about time management. My wife and I left Maui @ 6:00 a.m. and flew into Hilo (when they offered non stop back in 1998), picked up our car rental, went to Hilo airport to do a helicopter flight over the park, then drove ot the park. Yes, it is alot in one day but if you are strictly focusing on the National Park, then it should not be an issue. Then we left on the 8:30 non stop.