Banana, There is a very real possibility that they won't extend the window. I'm not trying to rain on anyone's parade, but would hate to see anyone banking on an extension that may very well not happen. I would strongly urge you to prepare assuming your center staff is correct that they're open tomorrow, then call in the morning to confirm and continue on to your appointment. If you call in the morning and they're not open, then call all day Sunday to try to get in touch and see if you can test Sunday. As bad as it would be for those who are testing at closed locations, there is a chance that NASBA would choose to NOT extend the window even if some locations are closed at the end of the window. Based on Banana's post and Positivethought's link, looks like at least 3 if not more locations are closed. NASBA could choose to extend the window based on these 3, but to make a national decision based on 3 localities may not be something that NASBA decides to do. If it isn't, then to not even try to go tomorrow would mean that you'd miss your opportunity to test. So, I would strongly urge you to proceed to try to test tomorrow (unless you go and they're closed or you try repeatedly to call tomorrow and get no answer), because if you find out later that they were open and that NASBA doesn't extend, or say only extends to Friday (and from what you've said, you wouldn't be able to test till Saturday), that would be very disappointing.
That being said, it is possible they would extend. In prior years, more than 3 locations were closed, so I wouldn't be counting on it yet…but they very well could. Only time will tell. So, still plan to take your scheduled tests between now and 11/30, but if anything changes between now and then, by all means take advantage of it if you're able to do so.