You can start 12/12 at 4 or 5 nodes or later. I have been trying to grow trees. When I should start a 5 nodes and grow short but huge buds instead of 3 to 4 foot trees If you start at 18/6 keep 18/6. It's a debate on 18/6 and 24/7. I have seen very little difference in the two but stay with what you start with