oh but it has been...

"Harvesting in the morning ensures that your plant will be at peak THC content, as cannabis has shown THC fluctuations peaking in morning and dropping during the day. Some growers leave their lights off for several days before harvest to increase potency. This seems to have some scientific validity as light has been shown to degrade THC, hence the morning peaks. As light is the degrading factor and the plant still has the ability to manufacture THC during darkness, leaving the lights off for a day or two before harvest likely utilizes the plants stored potential for THC conversion without any opportunity for it to be degraded into cannabinol (CBN) and other breakdown products"

Vic High, 2001. BC Growers Association. Web site and help desk.
The Cannabible, Jason King