I've read in most the articles within 2 weeks, perhaps sooner. The sex organs of the plant should start to show pretty soon.
Depends on strain, how long you vegged, and other conditions, but...anywhere from a few days up to 3 weeks, most folks probablly see sex in 5-10 days.
It went like this for me.. 1 week into 12/12 1 female showed 3 days after that 1 male showed 2 more days 2 more females next day another male waiting on last to show sex now at day 16