Originally Posted by williaty
Well, how long isn't the right question about warming it up.
The ideal warm up is to let it idle for 30 seconds or so, blip the throttle to about 50% of redline twice or so, then drive it gently while keeping it under 3kRPM until the oil temp goes over 180F.
Just sitting and letting it idle for any long length of time is bad for the oil and engine.
I heard similar advice from my cousin who is a total motorhead... know what the general theory behind it is??