Well if you run really fast, don't kill anything and generally get through levels as fast as you can I'm sure you could beat it in 45 minutes to an hour but I doubt 20 minutes.

Oh yeah the first time I beat the game it took me a week. But only because I played it in short bits completing about 2-4 levels each day. I cheated on the last 3 bosses and played on easy but nowdays I can complete the game on hard without cheating and in about 2 hours (the Devan and Bolly boss are real easy now)