I think if your a first time player it's not possible to beat the game fast. My fastest has been just over 50 days = 25 hours play time, pre Mistlands, but that was also employing a lot of things learnt from my previous play throughs and I think I allowed using some glitches to help me go quicker.

I'd say around 300 days if you went steady and didn't stuff around a lot for a first time play through so that could equate to roughly 100 - 150 hours playtime which if you get on a steam sale this game is worth it even at current full retail