It's probably safe to stay within the defined operating temperatures, but I have operated equipment out of spec before and it works fine. For example, my Canon A95 camera sees heavy use in cold conditions, so cold that moisture freezes on the LCD monitor. The camera still works fine, but it gets horrible battery life (once the batteries defrost, they work without recharging).
Basically, keeping it in the car once or twice in a pinch probably won't hurt, but I wouldn't do it too often.
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