Re: "cooling off": I've heard it's more about letting the exhaust valves cool a bit so they don't warp, and on old turbos, to let them cool a bit so they don't bake the oil in the bearing.
Never heard of a head warping/cracking due to temp variation from front to rear... that's just bizarre (I think unlikely- is the rear of the engine compartment 200 degrees hotter than the front? The engine is LIQUID cooled right?) and I'd be pretty PO'd at Volvo if that was true.
Here we are:
http://webcache.googleusercontent.co...d=ivns&strip=1
That sounds much closer to the truth.