By week 3 or 4, you should see the plants in pre-flower... by week 4 or 5, they should then be in flower... how long they go after that is completely dependent on the genetics and the conditions you provide. Don't, by the way, give them any nutes until about week 2 - they don't like them and, frankly, don't need them. When you DO start the nutes, start them about 1/2 strength to make sure they're going to tolerate them.
Good luck!