Some growers will tell ya that 18/6 benenfits the plants more then 24/7. Your plants do a quite abit of growing in the nightime hours as well.
The moment you change your light schedule from 18/6 or 24/7 to 12/12 your plants begin to go into flowering mode. You can start your countdown till harvest at that point.
thanks u all,... Ranger u jus answer my next Q i think, So that mean wait atleast 4 weeks to sex them right, and then i can revert back to 24/0 of light iz that right
Why revert back to 24/0? Are you going for a mother plant to get clones? The four weeks Ranger was talking about was 4 weeks of veg time at 24/0 before switching to flower at 12/12. From there it is another 8-10 weeks to harvest, and it spends the rest of it's time at 12/12.
If you want donor plants here is a good way:
when the plants are 1 month old and exhibiting alternating nodes, take a cutting from each one (label everything).
Root the clones (2 weeks) then put them into 12/12. In 2 weeks the male clones will express sex; toss them and their donors; bud the little girls out and you have female donor plants waiting to kick out more clones.