How long do you let you car warm up?

[OVERKILL]

I wait until the idle settles, which varies depending on the vehicle.

 

[69GTX]

Once the idle speed is reached, and the windshield is fully clear, off I go at approx 2,000 rpm/30-40 mph in a lower gear until the car's coolant temp reaches Normal Op Temp. That takes anywhere from 1-2 miles. Engine wear due to corrosive conditions in the oil doesn't taper off until the oil reaches somewhere in the 170-180 deg. range. IIRC the automaker wear tests keep the car running for extended periods at 140-160 deg F to measure the extent of cold temp corrosion/wear.