As long as you want. lol

I don't know anything about growing, but common sense would say that it depends on the strain of the plant and the conditions it's being grown in. It also depends on your personal preference (regarding the type of high you prefer from the bud - from what I gather, harvesting earlier or later can somewhat alter the potency and type of high).

The great people in the Cultivation section will be able to help you, like 3 Sheets To The Wind already said.

Good luck!