WP Feed Cache Transient Sample

gistfile1.php

<?php

function my_function_that_grabs_the_feed() {

	add_filter( 'wp_feed_cache_transient_lifetime', 'modify_feed_cache' );

	$my_feed = fetch_feed( esc_url( $feed_url ) );

	remove_filter( 'wp_feed_cache_transient_lifetime', 'modify_feed_cache' );
}

function modify_feed_cache() {
	return 30; // seconds
}