From the article:
Because individuals that consume a lot of cannabis, and consume it often, develop receptor down-regulation, building up a tolerance to effects of cannabis. In a research study, participants were given over 200 milligrams/day of THC everyday. In just twelve days, those enormous doses were no longer getting the participants uncomfortably high, because the density of their cannabinoid receptors was reduced in response to this chronic exposure. The good news about cannabis tolerance is that it appears completely reversible. Twenty-eight days of abstinence from THC has been shown in another study to up-regulate cannabinoid receptors to their normal density.
This seems interesting. No source as far as I can tell, but it seems to suggest that a 28 day T break would be enough for any user. Of course most people already knew this anecdotally, but it's nice to see something more solid.