Sunset at the end of the month is right around 6pm, so make sure you watch your time closely so that you are in Monterey before dark. You don't want to be driving through Big Sur in the dark - it's a bit sketchy in the dark if you've never driven it, and you'd miss the views anyway.
I took me about 6 hrs, it was beautiful
Map programs take you the fastest route, not the most scenic. You can usually force the route by dragging the markers or selecting a series of waypoints on your desired route.