Having owned both oilheads and airheads the manufacture advises to not let them idle for more than 10 minutes. That sounds like a good idea to me.
I always use a fan if I'm adjusting carbs, sync etc as 10 minutes can go by fast if you are preoccupied. If I'm stopped in a long line of traffic, like a railroad crossing, where you know you are going to be there for awhile I will shut the engine off, same as if I'm at a border crossing with long lines of traffic. Traffic lights and other similar type situations I let the engine idle.
Now if you want to talk heat the oil temp on my Softail has hit 270 F, 2 up in the mountains, lots of stop & go construction, 90 +F air temp. I run synthetic oil but that's too hot in my mind so I put an oil cooler on the engine shortly after that.
A certain amount of common sense has to be used when idling an air cooled motorcycle.
1971 R50/5 Cafe Project
2013 DL650 Adv