[NTLDR]

All you need is a simple cron script that runs every day (or at whatever interval you choose) to update the threads table.

PHP Code:

$DB_site->query("UPDATE ".TABLE_PREFIX."thread SET open = 0 WHERE forumid IN (X,Y,Z) AND dateline < A"); 


Where X,Y,Z are the forumids and A is the timestamp that the threads must be older than to be closed.