yes your plants will show sex as pre-flowers when they reach maturity, typically at around 4-6wks old from germ under 18/6 they will show either small female calyx's with two white hairs protruding out or small round balls for a male, but be carefull female calyx's dont always have the hairs or pistils at first and can be easily mistaken for a male, so if you see balls wait a bit longer to ensure no hairs come out and be sure its a male before you chop it or whatever. you can flower whenever your ready to really, just depends on what size final plant your after and what kinda yeild your looking for.....