I got across, the web console has a time out limit. The default is 30 min.
If you like to change you have just have to change i the web.config file. I will recommend to made a backup of the file first.
The default location is c:\program files\system center 2012\Operations Manager\WebConsole\WebHost\web.config
Search for <connection autoSignIn=”True” autoSignOutInterval=”30″>
If you set the value to 0 = unlimted