function scg_filter_feed_duration( $duration, $url ) {
if ( ‘http://shambhalatimes.org/category/featured-stories/feed/’ == $url )
return (3600 * 2); // every 2 hours
else
return $duration;
}
add_filter( ‘wp_feed_cache_transient_lifetime’, ‘scg_filter_feed_duration’, 10, 2 );

and if you want to improve it for all feeds:

function scg_filter_feed_duration( $duration ) {
return (3600 * 2); // every 2 hours
}
add_filter( ‘wp_feed_cache_transient_lifetime’, ‘scg_filter_feed_duration’ );