I spent the winter of 2014 working in the deep freeze of Fairbanks, Alaska, 300 miles south of the arctic circle. My job consists of driving either a 16ft box truck with a 4 liter, 4 cylinder turbo diesel; or a 26ft semi truck with a 6.2 liter straight 6 cylinder engine.
Due to the nature of 40 below zero temperatures, from the moment I unplugged my truck in the morning (from the block heater) and fired up the engine, I wouldn't turn it off until that night. No matter the mileage driven. Regularly the truck/s would sit for 3-4hrs without moving.
If you turned it off, you ran the risk of the oil congealing and not being able to start the engine again. It always made me uncomfortable to burn diesel all day long, but that was the nature of the beast.
On the haul roads up north, drivers have been known to start the engines in their semi tractors at the beginning of the freeze and not turn their engines off for 3-4 months at a time. NOT EVER turn them off. Not until the weather warms up.