A couple years ago we got up at 3 am and made the drive across Maui and up the winding road in the dark for sunrise here. This time it was just as beautiful (perhaps even better) coming up at the end of a fantastic day and witnessing the sunset. We stopped at a great restaurant on the way down the mountain and made a nice leisurely evening of it.
If you are planning to visit the summit of Haleakala I really do recommend bringing your cold weather clothes on the trip. Seriously, closed shoes, a wind proof fleece, a hat and maybe even gloves. Flip Flops and shorts don't really cut it.