You guys must not get very cold, I need lots of gas to either keep the car running while in the store, or an exstention cord to plug the car in. Winter here is cold enough to freeze and engine in not alot of time after shutting it off, were talking minutes.
We often have days that rarely rise better than -30 but that is no reason to have to keep the vehicle running. I shut my engine off every time I have to get out of the truck even for just a few seconds.
Once the engine is warm it stays warm unless parked overnight. When it has been parked overnight and temps are in the deep canadian deep freeze that we enjoy, I set the block heater timer for no more than 2 hours. If a vehicle needs more than that it needs a tune up or repair.
One thing that you may want to try is using synthetic motor oil. When I switched over to synthetic engine friction is reduced, and the engine starts up on cold morning starts like a warm day in july. And the nice thing is that the oil pressure gauge rises much faster than using regular oils.
Go easy on really cold starts, while a maintained engine is more than willing to go, the drive line and transmission are stiff and need to go easy for the first mile before friction in the driveline softens up the tranny and gear oils.