Dear Jan, you can change logout time by opening codelib/cfg/config.options.inc.php and do change in array:

//-- Specifies the time length to keep the log
define( 'SYS_KEEP_LOG_PERIOD', 90 );

90 - time to "autologout" in minutes (in your file maybe less)

Hi, SYS_KEEP_LOG_PERIOD has nothing to do with sesstion timeout. It's for debugging only.