Delay posts from appearing immediately in WordPress RSS feed. Source: http://wpengineer.com/320/publish-the-feed-later/

delay-rss-feed.php

<?php

//* Delay posts from appearing immediately in WordPress RSS feed
add_filter('posts_where', 'customprefix_delay_rss_feed');
function customprefix_delay_rss_feed($where) {
    global $wpdb;
    
    if ( is_feed() ) {
        $now = gmdate('Y-m-d H:i:s'); // Timestamp in WordPress format
        $wait = '10'; // Integer
        $device = 'MINUTE'; // MINUTE, HOUR, DAY, WEEK, MONTH, YEAR
        $where.= " AND TIMESTAMPDIFF($device, $wpdb->posts.post_date_gmt, '$now') > $wait "; // Add SQL syntax to default $where
    }
    return $where;
}