Look for what will appear to be either a spade shaped growth, or a teardrop shaped growth, usually up around the 5th or 6th branchset, and in the bract between the branch and the fan leaf sprout, right in that lil nook, is where these preflowers will be located. On the female preflowers, there will eventually be a little white stigma that starts to poke out of the top of the teardrop, and will eventually become a "V" shaped pistil, which is the trademark sign of a female. The males will usually resemble a ball on a lil nob. Very different, especially at later stages of the preflower's development... They r very tiny, at first, and takes many grows to become adept at knowing what u have. Usually in a tight grow, with CO2 systems, proper lighting, ventilation, temperature, and nutrient and water intake, the preflowers should end up showing around the 8th or 9th week of growth since sprout. Some strains reportedly don't or won't show preflowers until they r forced to flower, meaning their light cycle has been changed so that the plants receive 12 hours of darkness, on a somewhat regular basis... U can flower under 24 hours of light, as long as there's a break, regularly, for twelve, unbroken hours of darkness... But, its best for most growers to stick with the tried and true 12 on 12 off routine, and leave the playing up to the experienced-master gardeners...