You are growing autos so follow the instructions you can find everywhere around the world wide web : 18h of light from seed to harvest , 20h if you want, 24h will makes plants use more cal mag. If you want to grow under 12/12 the yield will be different from the other growers of this website . I am doing autos in 12/12 and my results are often lower than my grow mates who are under a classic 18/6 and when I finally have 70grams on a plant It can happens that I regret the fact I could not give her more light ( I am a outdoor grower , 12/12 is my outdoor natural schedule )