Maybe two hours for the second quest. This game's still great even after all these years. I completed Vs. SMB on 5/5/09 and All Night Nippon SMB in June 2008.
As posted, originally beaten in 1995. Have beaten the game several times since, including once in front of some of the residents of my college dorm in 2006. This was the first time that I had beaten all 32 levels without using any warps, continuing, or as Luigi. Not only did I break 1 Million points in the process, but I finished the game with [b]only one life left;[/b] the guy who was playing as Mario lost all his lives earlier. Talk about everything or nothing, grace under pressure, taking the bull by the horns; I would go on but I can't think of any more cliches!
This is a timeless classic that I would pick up and play again if given the chance.