I use it when I'm going somewhere for about 30 minutes or less. Any longer, and it is better to just turn it off except in extreme cold. The diesel does not use any electrical power when running so that should not be any problem. It only would use the normal key-off loads like radio memory, clock, parkng lights, etc. Even if the blower is off, the engine will always be completely at operating temp. making heating up nowhere as long as when you first start it.

I also keep my idle at 700-750rpm in the warmer months and 800-900rpm in colder months.