msec -> 시분초

     $days = intval($length / 86400);
     $remain = $length % 86400;
     $hours = intval($remain / 3600);
     $remain = $remain % 3600;
     $remain = $length;
     $mins = sprintf("%02d", intval($remain / 60));
     $secs = sprintf("%02d", $remain % 60);