You can go to 12/12 as soon as you have a rooted cutting of each plant, so when you know which one's the winner, you've got a mom ready to go.

Stinky's ( always ) right- look for the alternating node structure.

Not all plants will do this- I kept an Ortega for 5+ years that never went alternate. Trust me, she was blindingly mature.

Most will. Pre-flower development will also be a good sign.