The hana trip is definitely an all day adventure. You will see some beautiful country but it's a loooong trip.
As for the Haleakala bike trip, I think they have greatly reduced the number of those trips available. We did it seven years ago - travel to the top of the volcano around 3am to watch the sunrise and then bike down the mtn. We were dressed in layers (very cold at the top - think 20's) including full motorcycle helmets provided and minimal pedaling involved for the trip down over miles of switchbacks. Close to the bottom, our group was pulled over to allow backed up traffic to pass. DW was at the front of our bike group (arranged by height) and her bike slipped off a 6" shoulder down a 15' lava embankment, resulting in a 1 hour ambulance trip and a 3-day stay in intensive care at the Maui Memorial Hospital in Wailuku with a concussion and multiple contusions with months of recovery once we returned home. I was chewed out by the ER docs for attempting such a trip. This was on the first day of our trip. The staff was great and very compassionate but the adventure was not in any of the guide books.
If you do not suffer from motion sickness, try an airplane ride from Maui over the lava flows on the big island. Spectacular views, but the motion sickness issue is for another post. Don't ask...
If you want to see Haleakala, try the bus trip up and back. The view at dawn is spectacular. If you can find a bike trip, avoid it at all costs.