Quote Originally Posted by jolly green giant
you will have to wait till about 2 to 3 weeks after you change the lighting hours before you can start deciding the sex of your plants.
Just my opinion, 2-3 weeks is a bit of a "safe bet"
I'm a first time grower and spotted the males / females about..... 6/7 days after starting flowering.
Probably could of told earlier, but I was searching the lower nodes for signs not the top because I thought lower would grow first.

Yeah, males are pants unless you want to breed, I just hashed some immature males, wasnt nice, waste of time, gonna chuck them from now on.
Seperating the plants still runs the risk of accidental pollination, via touch, clothes, air, etc.
Plus, if you do that, you need to growrooms, twice as much electricity, plus you need more lights, ventilation etc etc etc.
From what I have seen personally, males + females grow at roughly the same rate, however this is my first grow, so maybe it was a one off.
As JGG said too, it's just the way they differ as well.