12/12 from begining. Even if it's auto flower they need some veg time. When they go straight to 12/12 the roots stop growing and they start to flower. You need roots. When you go to 12/12 they will only double in size or maybe just a bit more. You need a root mass to get good buds.

Oh and a sea of green is when you harvest half and then put new ones in for continual harvest every month or 2 weeks. I think you mean a screen of green in which you train them to go through a screen placed over them to fill up the area all the same height. Either way you can't because that takes even more veg time.