// Flush permalinks
add_action('vap_hourly_event', 'vap_do_this_hourly');
function vap_activation() {
    if ( !wp_next_scheduled( 'vap_hourly_event' ) ) {
        wp_schedule_event(time(), 'hourly', 'vap_hourly_event');
    }
}
 
add_action('wp', 'vap_activation');
function vap_do_this_hourly() {
    global $wp_rewrite;
    $wp_rewrite->flush_rules();
}