look very close m8, i spot the preflowers and leave it 1 or 2 days to make sure, "this making sure" is really me just coming to terms with the fact some of my best looking plants in veg being males , i know its male after seeing the preflowers, but i cant bring myself to part with it, just yet
then i do the dirty deed and kill the fuckers, those lovely plants killed because of 1 tiny preflower i can just about see with the naked eye,
i can say over the years it has never been wrong, even though i have wanted it to be wrong so many times
i take cuttings from the renaming female* (non preflowering male) plants it is possible that the non male remaining plants may show male signs later and be hemies but that is very rare, if that was the case i would just remove those cuttings
i do it this way so i can sex them early and then take clones from all the females before they have flowered
that way i don't lose the plant if it turns out to be a keeper, its quicker than rejuvenating a flowered female to get cuttings after harvest
preflowers come in veg from week 4 onwards on most plants i have grown some do not show them at all some show later, so i leave it to the first 3 days of 12/12 to sex them
keep looking for the male preflowers, you will see them before the pistals, they are easier to spot, you have to get your eye lol within an inch of the plants so close to see the male preflower forming, it will have a stalk, that is the giveaway sign
no female growth calyx growth has a stalk, you can see a little bobble on a stalk you know its male
you can spot premature cylax but they are harder to spot with the naked eye they are tiny, and have no pistils or just 1 pistil, the other pistal not emerged yet
if you have a scope it would make it easer i guess, but i have always done it without a scope
good luck m8