try this: 
open sources/misc/session.php
find:
	
	
	
		PHP:
	
	
		  $check_time = time() - 3600;
	 
 change to: 
	
	
	
		PHP:
	
	
		  $check_time = time() - 86400;
	 
 that should give you 24 hour login session, you can adjust the duration as needed.  We don't have a hook location for this so it cannot be done via plugin yet, but if you find this works I will add a hook here for upcoming release.