i would personally veg for 3-4 weeks under 24/0 and the flower under 12/12... you want to give your plant time to reach its full maturity... which takes about that long... now if you let your plants veg for 3-4 weeks and reach maturity, all the clones you take from it will already to be mature so you can start flowering those right after they root and get good mature buds... BUT... like i said, imho, you should at least veg for a few weeks before flowering.... bigger plant will give bigger yields... mature plants produce better buds.... so you could have 4 weeks veg + 9 weeks flower = 15 weeks total... or it could go 4 weeks veg + 6 weeks flowering = 10 weeks total.. it depends again on how fast the plant wants to grow and flower, the enviroment its in, and a ton of other determining factors... to make it easy, and quit my rambeling, assume youll have 12 weeks total from seed... 4 weeks veg and 8 weeks flower... thats if you veg, which is recommened, unless your using clones from a mature mother....