Meh, at least he posted in Newbie Central.
It all depends on how much you want to yield. If you don't want to have to buy ganja for a long time, then let your plant vegetate for 6 months and THEN flower it. If you're just looking to "give growing a try", or perhaps have a little personal stash of your very own home-grown, then give it a month or two, then induce flowering.