Add additional scheduling options to WordPress

add_filter( 'cron_schedules', 'my_add_intervals' ); 
function my_add_intervals( $schedules ) {

    // Add a weekly interval.
    $schedules['weekly'] = array(
        'interval' => 604800,
        'display'  => __( 'Once Weekly' ),
    );

    // Add a montly interval.
    $schedules['monthly'] = array(
        'interval' => 2635200,
        'display'  => __( 'Once a month' ),
    );

    return $schedules;
}