Quote Originally Posted by sonomacoma
i was wondering about how long it usually takes to show signs of flowering from when you switch light to 12/12
That depends.

I do 24/7 veg, followed by a week of 18/6 pre-bud before the 12/12 bud. I do this for root development prior to bud. During the pre-bud, total darkness is not crucial. I've had plants show sex during this phase - happened this grow - usually because I've vegged them too long.

During the 12/12 phase, every stray lumen lessens yield. If there's light brighter than a full moon, it'll retard flowering if not stop it altogether.

Once the 12/12 cycle starts, it can take anywhere from 1 day to 3 weeks to show sex, depending on strain & conditions. Usually about a week for males, and by 2 weeks the females. But this is NOT a hard & fast rule. I've had girls show before boys often enough to know that time into 12/12 is no indicator.