@wobit Good anecdote!My Woods-style coop is 6' wide by 10' deep, and has a small window on one side in addition to the top windows and the front windows. I'm in Massachusetts. Over the past 4 years we eventually block the top and side windows with only after the winter storms begin. We do not ever block the front, and sometimes there is a little snow that comes in, which doesn't seem to bother them or impair my deep litter bedding. While that's not a very precise recommendation, it's my anecdote that you can go quite late and be fine.
We did roof the coop with "suntuf" clear corrugated plastic panels to let in additional light and warmth and in winter when I rake the snow off, it does make it much brighter and more pleasant in there.
Do you have pics to post, please?

Does clear roofing overheat coop in summer?