$starttime = explode(" ",microtime());
$starttime = $starttime[1] + $starttime[0];
# тут скрипт.
$totaltime = explode(" ",microtime());
$totaltime = $totaltime[1] + $totaltime[0];
$totaltime = ($totaltime - $starttime);
echo " Сгенерировано за ".sprintf("%01.8f", $totaltime)." сек.";