PHPの場合。

function format_relative_date ($date) {
  $time = strtotime ($date);
  $second = time () - $time;
  if ($second < 60) {
    return ($second . "秒前");
  } else if ($second < 3600) {
    return (intval ($second / 60) . "分前");
  } else if ($second < 86400) {
    return ("約" . intval ($second / 3600) . "時間前");
  } else {
    return (date ("m/d H:i", $time));
  }
}