Leave the diesel running. I have an “02” Ford with 326k on it and I almost never turn it off. 14 hrs uses maybe 5 gals of fuel.
I read that while the Alaska Pipeline was being built in the 70's that had to do exactly that during the winter with the heavy equipment lest they find themselves unable to start them during working hours.OTOH,I'm on my third diesel and I've started all three in temps of -20F...-30F ...and even -40F.All three times were after the car had sat outside for 12+ hours.All three,in addition,were/are equipped with auxiliary heaters powered by the battery so the interiors warm up quickly.