It is unlikely that we will patch during the end of Decemeber. We like to have "all hands on deck" when we patch so we can respond to emergency issues as quickly as possible. Players in North America tend to think of it as "patch day" but for those of us at Blizzard, it's more like "patch week". One day we patch Europe, the next the US, then Korea, then China etc. -- all on different days (this is done so that we don't bring down their servers during primetime).
If you wanted an ETA, my best guess would be very shortly after New Years.