There is no "typical" closure date, but it hardly matters. All that means is that a portable "Road Closed" sign is set in the middle of the road at the start of the first switchback. People generally drive around it, and there are no legal consequences, unless you happen to be there when road crews are working on clearing debris. At some point during the winter it is likely that the road will be blocked by debris. And you will have to make your own decision about whether it's worth the risk driving up when bad weather is likely--you might not be able to get back down.