When does flowering start

I have 9 nice looking plants that were switched to 12-12 40 days ago. pistils, however took ~10 days to show, nodes were not alternating at that time. should flowering be considered to commence when the lights are switched, or when the pistles appear?

In your case when the pistols showed plz post pics

after the stretch and when the pistils start coming out in bunches is when flowering starts or when they get there little heads of hair

4th it when pistils start showing

He had no stretch

either way will work, give or take a couple days will not matter to the plant. just check the trichomes when the buds mature to know when to harvest.

Remember mostly cloudy head high amber to brown couch lock