Small script to place in child theme functions.php file to delay the publishing of a new RSS feed file.

delay_publish_rss_feed.php

<?php
//* Do NOT include the opening php tag


//* Delay the adding of new content to the WordPress RSS feed
function b3m_delay_publish_rss_feed($where) {
	
	global $wpdb;

  	if ( is_feed() ) {
    	
    	// timestamp in WP-format
    	$now = gmdate( 'Y-m-d H:i:s' );
    	
    	//* value for wait; + device
    	$wait = '15'; //integer
    	
    	//* http://dev.mysql.com/doc/refman/5.0/en/date-and-time-functions.html#function_timestampdiff
    	$device = 'MINUTE'; //MINUTE, HOUR, DAY, WEEK, MONTH, YEAR
    	
    	//* add SQL-sytax to default $where
    	$where.=" AND TIMESTAMPDIFF( $device, $wpdb->posts.post_date_gmt, '$now' ) > $wait ";
  	}
  	
  	return $where;

}
add_filter('posts_where', 'b3m_delay_publish_rss_feed');