Info from Wikipedia here.
This is the shot that almost wasn't. As I was was watching the subs being captured, I noticed a lot of trailing in them, like the guiding wasn't working. I fussed and I fiddled with the settings, even recalibrated the software twice. After I finally gave up and was putting things away for the night, I discovered that the locking screw on the guide scope focuser was loose. The guide camera had been moving around with the loose drawtube. Arrrgh!
Anyway, I managed to salvage enough decent frames to put this shot together. I can't guess how long it was, somewhere between an hour and an hour and a half total. Same setup as M16.