Blizzard will be performing scheduled maintenance on November 14th from 5:00 AM to 1:00 PM (PST). With this extended maintenance, no further details have been released. Since 7.3.5 is planned in a few weeks, it is possible this extended maintenance will be preparing for all of the changes that will be coming with 7.3.5.
As of right now, the build on PTR has not changed. Whether this will be a systems/hardware maintenance or patch prep remains to be seen.
This topic is continually updating. Keep checking back for more updates as we get closer to the maintenance time.