Some people might think that it is way to early to start thinking about winter tyres already during autumn, but it is too late to think about winter tyres when the winter already has arrived. It is definitely not safe to drive with summer tyres when it is winter outside. Therefore you need to start thinking about it and make sure you change early. I would say that if you usually have snow and winter conditions at a certain date, then changing a few weeks prior to that is a good idea. If you are really dependent on your car, this is a good idea.
It is always safer to drive with winter tyres a few weeks too early, than to drive with summer tyres a few days into winter weather. Safety should always be number one priority in the traffic. A lot of countries that have proper winter conditions have made it mandatory to drive with winter tyres if there I winter conditions. This should make you understand the significance of it. So put them on early enough and take them off when you are sure that the winter has passed.