I ran snow wheels and tires on my e34 for 5 years. I know how you feel. The only problem is if the temperature gets warm then the tires are too soft and squealy. As I hate changing wheels when it is cold, it is still kind of warm. I live in Chicago so I am not too far from you. I would change them when it was consistently under 55 for the high. I would at least wait a week or 2. When ever you change them, good luck with the the weather.