This is why 12/12 from seed IMO doesn't have any advantage over veging a month then flowering, unless you just want your plants to grow slowly. As dark said the plant wont flower before it is mature, plants mature when they are about 4-5 weeks old, so why not give them more light until then? Your plants will grow faster and be bigger when they do flower meaning you will have more bud and you will have grown it in the same amount of time. The only reason I can see for doing 12/12 from seed is if your grow space is vertically challenged and you want really short plants.