Ok, I'll stop short of calling it absolute fiction, but it's certainly a misunderstood rule of thumb.
It's a safe guidance, all strains will flower under 12/12, but it's not required. Most flower with 11 or less. Some strains can be given 15 hours of daylight and still flower!
The reasoning is genetic origins of different regions. The end of summer will be indicated by more or less daylight depending on your latitude. Those near the poles will see peak days of 24 hours! While those living near equator will never see more than 12.
Plants flowering in higher latitudes also greater swings. And winter comes with very long nights. That comes faster or slower.
All that means many learn to flower with longer days, knowing they are going to end quickly.
So that's the reasoning, what's the proof?
I've successfully run 13 hour flower cycles for strawberry cough and Jack Herer. I'm moving to try 14 hours of daylight for some Wi-Fi peyote that is vegging right now.
There's a timelapse video on my Twitter, can't upload it here.
