Cron job to delete threads without replies after a week?

[Vierie]

I would like to delete threads in a forum with no replies after a week via cron job. I'm not so sure about the variables. Would something like that work?

PHP Code:

$movedate = strtotime("now -7 days");    
$fromforuma="1";    // 1 would be the number of the forum
$DB_site->query("              
DELETE " . TABLE_PREFIX . "thread               
Where lastpost <= $movedate              
AND forumid = $fromforuma          
");