The Road to Hana. 620 curves, 59 bridges, ten to twelve hours if you stop — and stopping is the entire reason to go. Waianapanapa, the bamboo forest on the Pipiwai trail, the pools at Ohe’o, the banana bread stands. A guided version starts at $199 and removes the driving, which for many people is the better version.
Haleakala at dawn. An alarm at three, a reservation booked in advance, a coat in July, and one of the great sunrises anywhere. Also a two-hour drive up from the coast, which is the part people underestimate.
The west side. Lahaina, Kaanapali, the snorkelling and the beaches, and the northern loop road around the West Maui mountains if you like narrow roads. A day, easily.
Each of these is a day. The flight is a morning. That is the whole of the scheduling advice: four units, and most trips have room for three of them.