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function publish_later_on_feed($where) {
global $wpdb;
if ( is_feed() ) {
$time_now = gmdate('Y-m-d H:i:s');
$time_delay = '15'; // integer
$time_span = 'MINUTE'; //MINUTE, HOUR, DAY, WEEK, MONTH, YEAR
$where = " AND TIMESTAMPDIFF($device, $wpdb->posts.post_date_gmt, '$time_now') > $time_delay ";
}
return $where;
}
add_filter('posts_where', 'publish_later_on_feed');