it would only cause "sniffles" if those sniffles were to do environmental allergies like pollens or molds. allergies can last a long. long time so it would not be possible to make a general prediction on the duration of symptoms. cold breezes open windows will not cause colds. colds are caused by viruses and viruses last about a week.
sitting in front of a window unit cause sniffles? how long will they last when you move away from the front of the unit?