Yes, this is a widespread rumor. I can't really tell ya from experience, but I think it's true, considering the sources I've heard it from. The idea is that 24 hours of dark just kinda makes the plant panic and produce more resin in those last few hours. It's like one final attempt to get pollinated (which is what all the resin, etc. is for in the first place, in case you didn't know that). You wouldn't wanna do it normally since it stresses the plant and could lead to hermies, but in the last 24-48 hours, who gives a damn? The concept seems logical to me, though I doubt it's gonna make a HUGE difference... but a little more resin never hurts...