In ubbt.inc.php
Where the query is done to determine how many peopl are in chat - Above the query add this:
$LastOnChat = $this -> get_date() - 600;
600 seconds is 10 minutes.
Then alter the query a bit like this
$query = "
SELECT COUNT(*)
FROM {$config['tbprefix']}Online
WHERE O_Last > '$LastOnChat'
AND (O_What = 'chatheader' OR O_What = 'chatroom' OR O_What = 'chat')
";
That should do it independanly of Who's Online.
