Index: wp-admin/includes/class-wp-plugins-list-table.php
===================================================================
--- wp-admin/includes/class-wp-plugins-list-table.php	(revision 21206)
+++ wp-admin/includes/class-wp-plugins-list-table.php	(working copy)
@@ -74,9 +74,8 @@
 		if ( ! $screen->is_network ) {
 			$recently_activated = get_option( 'recently_activated', array() );
 
-			$one_week = 7*24*60*60;
 			foreach ( $recently_activated as $key => $time )
-				if ( $time + $one_week < time() )
+				if ( $time + WEEK_IN_SECONDS < time() )
 					unset( $recently_activated[$key] );
 			update_option( 'recently_activated', $recently_activated );
 		}
Index: wp-admin/includes/class-wp-posts-list-table.php
===================================================================
--- wp-admin/includes/class-wp-posts-list-table.php	(revision 21206)
+++ wp-admin/includes/class-wp-posts-list-table.php	(working copy)
@@ -573,7 +573,7 @@
 
 					$time_diff = time() - $time;
 
-					if ( $time_diff > 0 && $time_diff < 24*60*60 )
+					if ( $time_diff > 0 && $time_diff < DAY_IN_SECONDS )
 						$h_time = sprintf( __( '%s ago' ), human_time_diff( $time ) );
 					else
 						$h_time = mysql2date( __( 'Y/m/d' ), $m_time );
Index: wp-admin/includes/nav-menu.php
===================================================================
--- wp-admin/includes/nav-menu.php	(revision 21206)
+++ wp-admin/includes/nav-menu.php	(working copy)
@@ -1150,7 +1150,7 @@
  */
 function _wp_delete_orphaned_draft_menu_items() {
 	global $wpdb;
-	$delete_timestamp = time() - (60*60*24*EMPTY_TRASH_DAYS);
+	$delete_timestamp = time() - ( DAY_IN_SECONDS * EMPTY_TRASH_DAYS );
 
 	// delete orphaned draft menu items
 	$menu_items_to_delete = $wpdb->get_col($wpdb->prepare("SELECT ID FROM $wpdb->posts AS p LEFT JOIN $wpdb->postmeta AS m ON p.ID = m.post_id WHERE post_type = 'nav_menu_item' AND post_status = 'draft' AND meta_key = '_menu_item_orphaned' AND meta_value < '%d'", $delete_timestamp ) );
Index: wp-admin/includes/plugin-install.php
===================================================================
--- wp-admin/includes/plugin-install.php	(revision 21206)
+++ wp-admin/includes/plugin-install.php	(working copy)
@@ -74,7 +74,7 @@
 	if ( is_wp_error($tags) )
 		return $tags;
 
-	set_site_transient('poptags_' . $key, $tags, 10800); // 3 * 60 * 60 = 10800
+	set_site_transient( 'poptags_' . $key, $tags, 3 * HOUR_IN_SECONDS );
 
 	return $tags;
 }
Index: wp-includes/comment.php
===================================================================
--- wp-includes/comment.php	(revision 21206)
+++ wp-includes/comment.php	(working copy)
@@ -1976,7 +1976,7 @@
 	if ( ! $days_old )
 		return $posts;
 
-	if ( time() - strtotime( $posts[0]->post_date_gmt ) > ( $days_old * 24 * 60 * 60 ) ) {
+	if ( time() - strtotime( $posts[0]->post_date_gmt ) > ( $days_old * DAY_IN_SECONDS ) ) {
 		$posts[0]->comment_status = 'closed';
 		$posts[0]->ping_status = 'closed';
 	}
@@ -2011,7 +2011,7 @@
 	if ( ! in_array( $post->post_type, $post_types ) )
 		return $open;
 
-	if ( time() - strtotime( $post->post_date_gmt ) > ( $days_old * 24 * 60 * 60 ) )
+	if ( time() - strtotime( $post->post_date_gmt ) > ( $days_old * DAY_IN_SECONDS ) )
 		return false;
 
 	return $open;
Index: wp-includes/cron.php
===================================================================
--- wp-includes/cron.php	(revision 21206)
+++ wp-includes/cron.php	(working copy)
@@ -206,7 +206,7 @@
 	*/
 	$lock = get_transient('doing_cron');
 
-	if ( $lock > $local_time + 10*60 )
+	if ( $lock > $local_time + 10 * MINUTE_IN_SECONDS )
 		$lock = 0;
 
 	// don't run if another process is currently running it or more than once every 60 sec.
@@ -313,9 +313,9 @@
  */
 function wp_get_schedules() {
 	$schedules = array(
-		'hourly' => array( 'interval' => 3600, 'display' => __('Once Hourly') ),
-		'twicedaily' => array( 'interval' => 43200, 'display' => __('Twice Daily') ),
-		'daily' => array( 'interval' => 86400, 'display' => __('Once Daily') ),
+		'hourly' => array( 'interval' => HOUR_IN_SECONDS, 'display' => __('Once Hourly') ),
+		'twicedaily' => array( 'interval' => DAY_IN_SECONDS / 2, 'display' => __('Twice Daily') ),
+		'daily' => array( 'interval' => DAY_IN_SECONDS, 'display' => __('Once Daily') ),
 	);
 	return array_merge( apply_filters( 'cron_schedules', array() ), $schedules );
 }
Index: wp-includes/default-constants.php
===================================================================
--- wp-includes/default-constants.php	(revision 21206)
+++ wp-includes/default-constants.php	(working copy)
@@ -299,3 +299,31 @@
 		define( 'WP_DEFAULT_THEME', 'twentyeleven' );
 
 }
+
+/**
+ * Defines time related WordPress constants
+ *
+ * @since 3.5.0
+ */
+function wp_time_constants( ) {
+	/**
+	 * Constants for expressing human-interval intervals in their
+	 * respective number of 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 );
+
+	/**
+	 * Constants for expressing human-interval intervals in their
+	 * respective number of minutes
+	 */
+	define( 'HOUR_IN_MINUTES', 60 );
+	define( 'DAY_IN_MINUTES', 24 * HOUR_IN_MINUTES );
+	define( 'WEEK_IN_MINUTES', 7 * DAY_IN_MINUTES );
+	define( 'MONTH_IN_MINUTES', 30 * DAY_IN_MINUTES );
+	define( 'YEAR_IN_MINUTES', 365 * DAY_IN_MINUTES );
+}
Index: wp-includes/functions.php
===================================================================
--- wp-includes/functions.php	(revision 21206)
+++ wp-includes/functions.php	(working copy)
@@ -3220,7 +3220,7 @@
 function wp_scheduled_delete() {
 	global $wpdb;
 
-	$delete_timestamp = time() - (60*60*24*EMPTY_TRASH_DAYS);
+	$delete_timestamp = time() - ( DAY_IN_SECONDS * EMPTY_TRASH_DAYS );
 
 	$posts_to_delete = $wpdb->get_results($wpdb->prepare("SELECT post_id FROM $wpdb->postmeta WHERE meta_key = '_wp_trash_meta_time' AND meta_value < '%d'", $delete_timestamp), ARRAY_A);
 
Index: wp-settings.php
===================================================================
--- wp-settings.php	(revision 21206)
+++ wp-settings.php	(working copy)
@@ -23,7 +23,9 @@
 require( ABSPATH . WPINC . '/version.php' );
 
 // Set initial default constants including WP_MEMORY_LIMIT, WP_MAX_MEMORY_LIMIT, WP_DEBUG, WP_CONTENT_DIR and WP_CACHE.
-wp_initial_constants( );
+wp_initial_constants();
+// Define time related constants.
+wp_time_constants();
 
 // Check for the required PHP version and for the MySQL extension or a database drop-in.
 wp_check_php_mysql_versions();