When to turn on oscilatting fan?

Hi guys,

I was hoping someone could give me clarification on how early I can start run my oscilatting fan in my tent. All of my autos have just sprouted and one is over a week old now. I'm sticking to the humidity levels recommended for this stage (65%-85%) in Chris's book, and I saw a little bit of mildew in the tent today. I know an oscilatting fan can help prevent this but I wanted to make sure not to harm the new sprouts. TIA!