How long did you veg them for? If they were vegged long enough, you can look at the pre-flowers and sex them that way. If there aren't any pre-flowers to check, you naturally have to wait to see sex. I myself have had pistils emerge in as short as the next day, and I've also seen guys on here that have waited up to two weeks for their plants to show sex. That's the beauty of checking the pre-flowers, you don't have to waste a week, or even more sometimes if it ends up being a male.