Unless you have spent your entire life in flat country with no winding roads, you will have no problem driving it - just be sure the driver doesn't spend too much time eyeing the scenery!

Can't remember how long it takes - I'd give the entire round trip 3 hours, though, in case you get a great view at the top and want to spend some time.
If the day is cloudy, though (overcast), choose another sightseeing locale on Maui. We learned this the hard way - twice in one trip.