Hi,

I guess (!) that’s set in the php.ini (which is not accessible on a shared host).
Upload this script to the server and call it:

<?php
  echo '<pre>Session Lifetime:              '. ini_get('session.gc_maxlifetime')."<br />\n";
  echo 'Garbage Collector probability: '. ini_get('session.gc_probability')."<br />\n";
  echo 'Garbage Collector divisor:     '. ini_get('session.gc_divisor')."</pre>\n";
?>

PHP’s default for the session’s lifetime seems to be 1440 seconds (24 minutes). If you want to change it, locate the line

session_start();

in index.php and add the line

ini_set("session.gc_maxlifetime", "X");

just before, where X is new lifetime in seconds. Untested (I don’t entertain mlf2.x)!
In my installation I have set it to one hour.