Rick; Chances are you probably didn't hurt it since it was that warm outside, but, it didn,t do it any good either. I know there many that will disagree with me, but here goes anyway. The diesels on most mobile equipment such as tractors, pickups, and even big trucks and heavy equiptment are really not meant to idle that long at low idle speeds. Everyone sees the diesels sitting there at what you think is normal idle speed, it likely isn't. Think of it like this, a diesel uses compression that produces heat to run. You hit it on the nose saying that you left it at low idle to cool, that is exactly what it does, now think of this, if that engine basically runs on heat for combustion, isn't it logical to assume you could carbon the engine up ? Also you produce condensation that we all know you don't want in your crankcase.
My Powerstroke even has a feature to prevent this at idling around 30 degrees and below. The time frame appears to be temp related, but it will kick the idle up to around 1000 rpm to keep the engine temp up. That is what most people don't see.
As far as diesel generator goes, yep they'll sit there for days at generating speed, but that is way above an idle. You actually cool them by going to an idle.
I hope your not one of the **** types or you'll be out there changing all your oil and filters and flushing the engine at least three times.
After all this, you probably did no real harm but like I said, you did no good either. Just don't make it a habit. It sounds like you won't.
Come on people, I know someone will disagree.
My computer, my dime.
