[Logician]

edit showthread.php, find:

PHP Code:

$bbcodeon=iif($forum[allowbbcode],$ontext,$offtext); 


Before that add:

PHP Code:

$join_today_dif=mktime (date("H"), date("i"), date("s"), date("m"), date("d")-X, date("Y"));
if ($bbuserinfo[usergroup]==3 AND $bbuserinfo[joindate]<$join_today_dif)
{
 show_nopermission();exit;
} 


Replace X with the day number you allow them to access threads.

Not tested but should work.. Enjoy..

Logician