How times change.. When I was a teen ideling of Gasoline engines for more than a minute or two was not recommended cause the plugs would foul. In fact when I went to work for the State of Michigan at 27,, One of the things that was common on the freeway was for suspects to rabbit (HIT the gas and try to flee) when the troopers "Lit 'em up" (Turned on the police lights) because the city police cars which normally operated the streets at low speed... Well the plugs fouled and when they tried to catch the violator.. The engine would buck, stutter and stall often as not. (Sadly for the violators the State Police cars did not have that problem since they only traveled about 3 blocks on surface streets then HAMMER DOWN time on the freeway)
Diesels of that era however could idle all day no problem
Today... Thanks to modern Engine Control Comptuers, Gasoline engines, can idle all day (in many cases) no problems (Some of the big ones may overheat)
Diesels, however,, have a need for speed (more than idle).
The proper warm up time for all engines is the same.
Start engine,, Buckle seat belt, Engage and SLOWLY drive out of campground.
By the time you hit the road, you are warmed and ready to hammer down.