put them on 12/12 when ever u want , yes there gonna double or triple in size but i would grow it out for a few months on 18/6 to get a decent yeild because it takes a few months to get your harvest when u go 12/12 might aswell milk it.IMO there is no point of going 12/12 b4 a month because your plant wont start to flower regardless of light hours until it has matured