Back in the old days where we had mechanical diesels with no glow plugs, idling was necessary, especially if in the dead of winter, if shutting it down meant having to go through the pain of starting it back up with a shot of ether or such. And I remember my old man used to get mad as heck when I'd shoot too much starting fluid in an old diesel. It sounded like it was coming apart, and it probably was. Also the issue of fuel gelling in lines if it wasn't being recirculated by the fuel system. Plus the accepted thinking that the engines were built to last and idling "shouldn't" hurt them.
Different attitudes towards idling depend on the type of business you in and what part of the country. My sister has worked for UPS for 20 years. Those engines in the package cars are started and shut down a hundred times a day and hold up remarkably well. Many of those trucks have the same basic Navistar 7.3L equipment I have in my Ford truck. Besides the liability of leaving a truck with open access idling out in the street, their line of thinking is that starters are cheaper than fuel over the course of a couple hundred thousand miles. And idling of feeder tractors is restricted by ordanance in a lot of places and there's less need to idle when most of the time you are loading or unloading. But policy says no idling even when hooking or unhooking trailers so you shut it down if you get out of the tractor. I used to work for a trucking company that did a lot of OTR hauling for UPS and we had to follow the same basic rules.
FWIW, the less-than-truckload LTL company I drove for who owned their own trucks had a 2 minute policy. That to me seems like a good balance and one could argue that a 1 minute policy makes even more sense. They maintained their trucks well and they seemed to last forever. The old Volvo tractor I started out with had 750K miles on it and ran great, not using much oil at all, with no major engine work to speak of. But every tractor I drove with around 400,000 miles on them at a OTR company that leased them were practically junk.
And the over-the-road company I drove for idled a lot. Drivers live in those trucks and in order to maintain creature comfort in temperature extremes, you idle to keep it warm, and idle to keep the A/C running. A gallon an hour a Detroit Series 60 consumes at idle. So idling was more or less accepted except in states that have anti-idling rules in place. Those trucks are leased and they aren't well maintained. Nasty doesn't even describe some of the tractors I've driven. Many burned excessive oil and endured extended oil change intervals in order to save money.
I heard wet-stacking mentioned. And there's plenty of info on that around the internet. So won't cover it here other than to say it wouldn't be a problem on an engine idled for a minute or two, especially if it's at operating temp.
So in my experience (worth $.02), a minute or two would is a good balance.
