Maybe not an overnight mash, but an all day one. Mashed in at 4:30 am, hit a temp of 156* on the Halcyon Wheat kit from NB. In a 5 gal cooler set up, I dropped to 139 after 15 hours. (Damned kids take up even more time than I had planned for.) No souring that I could detect, fermented from 1.054 to 1.007 with US-05. Should be carbed in a week or so.
I am not sure how much time this saves me, maybe an hour or so in the evening. But in my case, with kids and wife and the rest of the American Dream to contend with, this method forces me to brew the beers I know I want to get brewed, when the weekends are just too booked up. I'll do it again for sure. From all the reading on forums I've done, it sounds to me like this method can be used for either clean beers or sour ones. Just comes down to temp management.