Flower day

I consider the early flip a "transition" period and call it flowering when you see the bud sites forming. Some strains transition faster than others but on average it's about 2 weeks. Look at your cola tops, they'll start looking different as they turn into a flower.

Day of light change. Photoperiods will be done 8 to 10 weeks from light change.

With autos, when you see pistols forming, photo periods start at the switch to 12/12

I've been thinking the same thing. I've started the counting a day or two after I've switched to 12/12 light cycle.