your looking for preflowers. i forgot when mine appeared. ima guess and say week 6 of veg maybe. i was super busy at th time and i still veged the damn thing for 6 months. under 4ft flro and all of my clones have preflowers so idk there time line either
You can start 12/12 whenever you feel like it man. When growth begins to slow and you have maximum bud sites, well then its about time.
Also you will start to see male or female preflowers