Actually, the average car at idle takes around 1/2 gallon per hour of fuel, so even at 10 minutes to warm up, you are not approaching anything that would be a large negative impact on fuel and the benefits of a warm car for comfort are added also.
Note: For your own "safety", do not-under any circumstances-let GM hear / see you say this! They will go ballistic! Irrational, yes. But lawyers / gov't (same thing?) abound! They want you to "drive off"...to conserve fuel. Disregard your poor ring / cylinder wall interfaces being washed down with unvaporized gasoline! Wear, wear, wear out!
That's pretty much one of the major points: Warm-up time is halved by driving vs. idling.
Hmmm.... I thought engine loading had something to do with ring-loading! Guess I am wrong.... Me? I'll continue to warm up my engines until the water temp. needle moves...like BMC (used to?) recommends! My rings/cylinder walls will continue to love me! LOL!