I've been running synthetic oils in my entire drivetrain, since my 4Runner was only a few thousand miles old. In bitter cold temps, say -30° F, I'll start it up, and if I didn't have the block heater plugged in, I'll let it run long enough for the oil to circulate, say 30 seconds. Then put it in gear and drive gently until all of the drivetrain components have some heat in them.
I've been using that method for 17+ years now for the 4Runner. It still runs like new.
Sitting there idling for longer periods of time, just wastes fuel. With the engine running rich for long periods, the excess fuel being injected is also more likely to get past the rings, wash down the cylinder bores, and dilute the oil.
A so-called dynamic warm-up, wherein you start driving gently after minimal run time, warms the engine and the rest of the drivetrain up much more quickly. That's better for the engine, it reduces your emissions, and you'll have heat sooner too.