Something that always bugged me about the TYPO3 backend was the message „Your session may have expired. Do you want to login again?“ after every hour I was idle, so I looked for a solution:
All you have to do is to set following in your typconf/localconf.php file:
$TYPO3_CONF_VARS['BE']['sessionTimeout'] = '7200';
This will set the backend session timeout to 2 hours.