The length of time varies depending on how much money you have to invest in quality lighting. Real good light can get you to sensi bud in less than 5 months. Maybe less However, to do it that fast you have to do just about everything correct - mistakes = stunted growth and stress...

If you're just starting on a large scale it might be wise to get good at it before investing a lot of money only to end up with root rot or a bunch of hermaphrodites that will spoil your harvest to seed etc...

Good Luck