If I talk myself into going out in severe cold, I can usually last two or three hours. It takes a commitment just to buy the right clothes, but that's OK. The last couple days here have had windchills below zero, but it IS the end of the season. And a long wait 'til next September. My personal coldest hunt was at -30. I went in a bit later than usual, getting on stand right at pink light. Within an hour, I'd rattled in and killed a small buck. When I saw the hit, I immediately got down and went to locate the buck. The blood-trail was already frozen over and pink,instead of red. Field dressing with bare hands wasn't alot of fun,though.
My coldest 3-D shoot was in central Wisconsin a number of years ago. As the sun started to come up,the temp bottomed out at -42! The targets were out overnight, and guys were breaking off cedar arrows trying to get them out of the foam. There was a huge bon fire half way though the course. We had a blast.