I've ridden my bike in the typical bike outfit (spandex shorts and shirt) in below freezing weather - once you've warmed up to it, it's actually much more refreshing than during hot weather. Going another 40 degrees below freezing would make it very uncomfortable, but as long as you had good circulation, kept your extremities moving, and worked hard enough to heat your core and muscles, you could probably handle it for an hour, and chances are good he was going more than 4 miles an hour, so it may have only taken him 45 minutes or so.