Hello. Yes, It's been studied. There is an increase in THC with 2 days of dark before harvest. And then a slight decrease on the 3rd day.
When I was at the Grow Up conference a couple of years ago, I asked the lighting expert after his talk when questions were answered.
He said it's really hard to do the dark thing in a hugh greenhouse, but he does the dark thing for his own personal plants.
Yes it works.
Chuck.