It doesn't take very long for an engine to warm up the oil to useable viscosity, if it did your engine would not last long. The biggest issue, other than the engine and window fog is transmission oil, as it doesn't warm up from the engine's bang bangs. But it isn't going to warm up much sitting still, either. So you want to take it easy in the first few minutes of driving so that transmission fluid moves around a bit and it will generate it's own warmth.
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