This downtime is for general maintenance and is effective tomorrow (Monday):

Guessing by the amount of online carnage that ensued, it appears everyone enjoyed the launch weekend of Warhammer Online. Now we need to do some work on our end to make sure the WAR keeps going full tilt. We will be bringing all of the servers down at 9:00 AM EDT on Monday, Sept. 22nd in order to do server maintenance. We estimate that the servers will be back online by 1:00 PM EDT. Check back here for updates and, as always, we thank you for your patience.

Click here to view the announcement at the WAR Herald.