i'm new to growing myself but what i have watched and red your better of vegging those plants for a month or so and take clones from them..then once the clones start growing nice and have a root system u can flower these to see if you plants are males and females.

my 2 plants showed signs of female hairs after 3 weeks of 20/4 light, so either wait a couple more weeks for signs or just take clones from the 3 plants u have.

gl