There are 3 variables that effect the time for muscle growth. Diet, rest, and the stimulus. The more stimulis you have (volume or sets), the more time it will take your muscle to grow (assuming diet isn't a factor). This is why I do not understand the high volume 6 day/ week workout. Your muscle needs time to recover from the workout and additional time to compensate for the growth. The more sets you do with less rest days will cause your body to go into overtraing at an expotientially fast rate. With the high volume method, most people don't give thier body the time off it needs- hence all the "plateau questions" I see on the board.