Out of curiosity on your Barbarian and Wizard did you use your preexisting gold from your Demon Hunter to buy really good gear from the auction house right away? That could be the reason for the timing going down so drastically.I would consider myself a hardcore player one of those guys that takes a few days off when a game like this or a WoW expansion releases. With that said my first character was a Demon Hunter that took 57 hours and the course of a week to complete. My second was a Barb 49 hours and 5 days, and last but not least my wizard which took 3 days and only 37 Hours
1st DH = 57hrs
2nd Barb = 49hrs
However a great deal of the hour drop in my leveling time was simply me getting more familiar with the game, it's mechanics, and the general course and layout of the game to cruise through it quicker.