In the nineties, diesel one ton pickups became REALLY popular here in Texas Ranch Country. I had one for quite awhile myself for pullinig a cattle trailer and a gooseneck flatbed for hauling hay and equipment.
Now they are so common, it's not unusual to see a 90 pound lady drive up in a four door, long bed, dually diesel and almost need a ladder to get back in it after parking it at an angle taking up two parking spaces by the front door of the store.
I THINK that it's the fact that these folks see the 18 wheelers at the truck stops idling during lunch, so they think they have to leave these noisy things running all the time. I guess it makes them feel like Cannon Ball Jones or something. Whatever is causing it has things out of hand in this area.
Saturday a week ago, my wife and I went to a little, local boondocks cafe for a liesurely breakfast. It was a beautiful morning and the windows were all open in the area where we were sitting. We had just gotten our coffee and some Cowboy drove up and parked with his exhaust pipe pointing right at our window. He left it running and came in and sat down. I was just about ready to say something to him, when someone even more beligerant than myself asked him if his starter was out. The driver didn't get the hint, so the guy said "would you please shut that noisy thing off?" He went and shut it down, but by that time we could barely breathe. We moved into the smoking area which was easier to deal with than all that diesel smoke lingering in the previously fresh air.
To answer the question of the OP, in the owners manual for my new 5045D it says do not idle it over five minutes. I don't know if your owners manual says the same, but it sounds like quite a long time. It's not good for any engine to idle more than a minute or two when it is necessary, like at a stoplight.
My $0.02,