You do not want to start your plants in 12/12. A 12/12 photoperiod would force the seedling to sprout and go straight into flowering. I remember pics on o.g. of an experiment on this. It was a very very tiny plant and yeilded less than a bowl of bud.

You should read the boards, perhaps buy a book or two. Its a fasicinating plant. If you love to smoke and are even considering to grow, research now and the more effort put in now will save you 100s of failed attempts.