Clearly, some people have no idea what actually happens in a shop. If you are crazy enough to think they are driving every car around for some significant length of time to hear up the fluid, please don't drink kool-aid.

A run through the gears and letting it idle will bring it to temp quickly enough, without the possibility of accidents, etc. If you wait until the cooling fan has cycled twice, you will be as close as you need to get, but 80C at the pan is good.

Remember, there is no thermostat in the transmission. So at 20°F, how long would you have to drive to ever get the fluid to operating temp?

That's the point. Either you are doing something to follow a process tied to a standard, or you are just guessing. And if you are guessing...