A little over is probably better than a little under. But that likely won't make much diff either way. As for the total darkness thing, from what I've read, the difference between 99 percent lightproof and 100 percent lightproof can be as much as 30 percent difference in yield. Whether that's true or not, I do not know, but it doesn't hurt to assume it's true and do everything you can to keep all light out. But even if you don't, you'll get some yield. If you're in the selling business, that could be a considerable financial difference if that's true though. I go to some pretty crazy lengths to keep light out, just in case that IS true.