Depends on the environent.
I was thinking switching the Arduino at room temperature might have an effect but most people seem to think it will not or be negligible. I had not considered that the ambient temperature might be quite low, in which case it probably would have an effect.
Does anybody know what the normal running temperature of an Arduino is if the ambient temperature is 20C?
If the Arduino had reached its peak temperature how long would it take to cool to the ambient of 20C?