This functions fetches and refreshes the data if needed.

pb_get_news.php

<?php

function pb_get_news() {

    /*
     * Get transient and if expired refresh data immediately
     */
    if ( false === ( $news = get_transient( 'pb_bbc_news' ) ) ) {

        // Uses BBC News API to fetch new data
        $news = pb_refresh_news();
        
    }

    /*
     * Check if News has soft expired, if so run refresh after page load.
     */
    elseif ( $news->expiry < time() ) {

        // Add 60 seconds to soft expire, to stop other threads trying to update it at the same time.
        $news->expiry = ( time() + 60 );

        /*
         * Update soft expire time.
         */
        set_transient( 'pb_bbc_news', $news, 24 * HOUR_IN_SECONDS );

        // Set the refresh function to run just before PHP shutsdown.
        add_action( 'shutdown', 'pb_refresh_news' );
        
    }
    
    return $news;
    
}

?>