According to Google Maps, it takes me about 5.5km to notice the needle starting to come up. That's driving on 50 and 60km/h roads, temps around -20°C to -25°C. If it's really bad stop & go, then not for a little while after then until I get onto the 80km/h roads. I usually leave the car in a higher gear and let it rev a bit higher so it doesn't lug and it warms up quicker. I can't plug my car in during the day while I'm at work without paying an extra $3/day for parking (no thanks!), but I have never been stranded because my car wouldn't start. Credit where credit is due to the VW engineers that made a diesel engine that starts in truly bone chilling cold!
I read somewhere on here a REALLY good tip that actually works for starting in the cold when it's not plugged in and/or has been sitting a while (even in the summer). When you first get in, just crank the key straight to start without waiting for the glow plugs, but just a couple revolutions is all it takes (like.. whir whir is enough, less than a second) then shut it off. Now do the glow plugs and when they're done, it will fire right up with minimal cranking. The theory behind it is that the fuel either drains out of the injectors into the cylinder or back into the IP and they lose their prime so doing a couple revs with the starter will reprime the injectors and make firing it up much easier. I've been doing it every afternoon after work and man does it make a difference in starting! I don't need to in the morning because my Zerostart and battery blanket have me covered. If you have a hard starting car anyways, you likely have other problems that need to be addressed, but the reduced stress on the starter is always a good thing. As always, YMMV but I'm getting along pretty well with this little trick.
Big time kudos to whoever suggested it in the first place. If only I remembered your name or the post!