Even though I'm just from North Dakota.....

Quality fuel and keeping the tank full are the keys for winter fuel. For me, most of my winter starting of small diesels is with ThermoKing (60hp Volvo) engines, which don't need to be plugged in until colder than -30F, if they have synthetic oils, provided they're run nearly daily and have a good battery. The length of the fuel lines is about two car lengths, so this ought to work in a car: start mixing fuel (#2/#1) at 32F. 50/50 by 10F, straight #1 by 0F.

Note I said quality fuel, which means active truck stops and active Cenex.

"Winterized" fuel means #2 with additives added at the station.
Who are you going to trust when your paycheck depends on a running engine?
Active stations and keeping the tank full means less condensation in the tank (yours or the station's).

Once the fuel's good then it's the battery's turn.
You need to glow the snot out of it when it's cold. 5min is not too long when it's -20F. Remember, the hotter the plug gets the lower the current draw on the battery. Now you probably have one chance to start the engine, because a cold and stiff starter is going to take the rest of the juice. So crank it and keep cranking up to 10sec after the engine begins to fire. Slowly step into the foot throttle just before you let go of the starter. Hold the foot throttle until the engine is running freely, because the other cold stuff (transmission, power steering, etc.) is going to put a big load on the engine. And thank your lucky stars if you have a manual transmission.

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daBenz - 1970 220D