the answer to your first question is yes...The 12/12 light cycle will flower the cuttings, but you're looking at at least 3 week until you MIGHT be able to sex them "properly"...

Assuming that the cuttings root (and live). Obviously there has to be males and females (well... all females are ok too, as long as you can get them to hermie). You can't really "leave them to their own devices" either. If you want a good amount of seeds that will produce worthy offspring, you have to take care of these plants and this room as well as you do any other.