You are not supposed to idle your truck at all. Of course, no one pays attention to this law and apparently no one enforces it, either. That's a good thing. I'd like to ask the people who come up with such laws how they would feel if I went into their home and turned off their furnace or central air conditioning. I don't think they'd be very receptive.
Some drivers idle their trucks all day, every day, no matter what the temperature is.
This is a waste. If it is a nice day I do not run the truck. If it is freezing or blazing, though, the truck is most certainly running. I got a good night's sleep and loaded out of Lakeview, NJ the next morning. The load went to Crete, NE .