From the Wizard 101 Forum :
Wizard101 has a regularly scheduled maintenance of 3am to 4:30am Central US time. On June 05 2009, we will be performing maintenance during this time, and players will not be able to log in. Thank you for your patience while we continue to improve the game for all our players.
So if you ever see that little symbol at the bottom left corner of your screen that says "you gotta log out in such and such time", dont worry. :)
Your Wizardly Advisor