From my understanding, thats when it builds up resin. "when the lights are off.."
I've even heard more than one person say if you take 2 plants of the same strain and growing conditions and leave one in 36hrs of dark before chop and 1 just let it go for the 12 hours.. Supposedly the longer dark period before chopping increases the resin production, I haven't had any direct experience with this method yet but I plan to try it eventually...
As for the dry box, you should be fine! Make sure you get some pics up when you harvest
I want to give it a look..
Oh and one more thing, I tried trimming the "sugar leafs" before and after the bud dried and it seems to be a lot easier to just do all the trimming right after you take it down. Plus let her dry out for a few days before you harvest because that will cut down on drying time!!! Let us know how it goes and good luck!