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));
  }
}