growing weed fast and quick

ok hey everyone listen to this and tell me how i can do this, i got a basic flourecent light tube, and i set it up for growin and i got a few plants that sprouted , anyways i am gonna stick them under a light , 24/7, but how long do i have to wait before i can switch the lighting to 12/12 i dont want a big plant i want a plant that is just old enough to flower , i have heard of flowerin a plant that is a month old , is this possible? peace out and thanxs for all comments, btw sorry for not postin lately, its been a crazy summer for sure