The Seven Pools is an all-day adventure. You can ask the concierge for a map. It will be numbered and have you stop at all sorts of cool sites on the way to the Seven Pools.
Haleakala Crater is amazing. I believe you can make reservations three days in advance but check the website. You will have to leave SUPER early in the morning, but the stars are amazing and so is the sunrise. If you can't make reservations or you aren't interested in waking up that early, go for sunset. We have never done this but heard it is equally cool! It is freezing up there so you will need thick jackets, gloves, and hats.
If you’re up for an adventure, the Road to Hana is a must! It’s a beautiful, twisty drive through Maui’s rainforests with waterfalls, beaches, and amazing lookout points along the way. Pack snacks, take your time, and enjoy the ride, getting there is half the fun!