$res .= sprintf "%dw", $weeks   if                                $weeks;
 $res .= sprintf "%dd", $days    if                       $days or $weeks;
 $res .= sprintf "%dh", $hours   if             $hours or $days or $weeks;
 $res .= sprintf "%dm", $minutes if $minutes or $hours or $days or $weeks;
 $res .= sprintf '%ds', $seconds;