PHP 秒数(分/時/日/週/月/年)を定数で定義するメモ

WordPressコアファイル内 \wp-includes\default-constants.php の121行目にも分／時／日／週／月／年の秒数を定数で定義しているところがあります。

/**#@+
 * Constants for expressing human-readable intervals
 * in their respective number of seconds.
 *
 * Please note that these values are approximate and are provided for convenience.
 * For example, MONTH_IN_SECONDS wrongly assumes every month has 30 days and
 * YEAR_IN_SECONDS does not take leap years into account.
 *
 * If you need more accuracy please consider using the DateTime class (https://secure.php.net/manual/en/class.datetime.php).
 *
 * @since 3.5.0
 * @since 4.4.0 Introduced `MONTH_IN_SECONDS`.
 */
define( 'MINUTE_IN_SECONDS', 60 );
define( 'HOUR_IN_SECONDS', 60 * MINUTE_IN_SECONDS );
define( 'DAY_IN_SECONDS', 24 * HOUR_IN_SECONDS );
define( 'WEEK_IN_SECONDS', 7 * DAY_IN_SECONDS );
define( 'MONTH_IN_SECONDS', 30 * DAY_IN_SECONDS );
define( 'YEAR_IN_SECONDS', 365 * DAY_IN_SECONDS );
/**#@-*/