Hello my friend so many growers do that with the dark phase because they say that in the dark they concentrate entirely on the production of Thc and other active ingredients. Through these 2 nights the resin production would have to increase. Because you can't prove it scientifically (every strain is different). I prefer to make my harvest immediately in the first few hours of my lighting plan. When you harvest you can see that the essential oils, aromas, terpenes etc. are of the best quality.