I've had females poke out their hairs in week 6 or so. However it's not a 100% depended on method, because all strains are different & all growing environments are different. The best and most assured way is to clone and place into 12/12. A "mother" plant is one known female, that you designate for cloning purposes only. Like I said you have to know that the plant you are planning to use is a female. The plant won't be as strong as it could be, if you switched it to 12/12 and then revegged back to a mother plant. This is why you take a cutting, and get a loop to see clearly...