Hi, I personally do 18/6, but either will work. The first couple of days close the vents and gradually open them up. Also give the plants some time with the top off for a few minutes a day—- basically just to spray some water on them. The most important thing with cloning is keeping the tray warm with a seedling mat, taking the cuts right and clean near a node, and using some sort of rooting hormone. Not much to it! I’ve even cut off a top of a plant and just stuck in the dirt and it cloned! People over think it! Good luck ✌️🏻💚🌿