fans - stem growth

when you all talk of having fans on for stem growth - are you all implying it be on constantly - is say one hour a day enough?

My grow box is near an open window - some fresh air gets in but does not circulate much - so will a fan for one hour a day do the trick to get the air moving enough?

i would put a fan on it constantly if u think about in nature the wind is blowing constanly

but don't have your plants like their in a tornado just a steady gentle blow