I’d suggest you focus on one side of the island if that’s all the time you have. We did the Hilo side, including Volcanoes NP in 3 days; then we did Kona aide in 2 days. As it was, we felt like we were rushed. One highlight for us was the helicopter ride from Hilo over Volcanoes NP. We had already stayed at the park and explored during night and day. But the helicopter tour gives you a great perspective you wouldn’t otherwise have.