// Schedule Cron Job Event
// Custom Cron Schedule Interval



function auto_post_job_function_own( $schedules ) {

    $schedules['post-change-24-hour'] = array(
         'interval'  => 12,  // 86400
        'display'   => __( 'Custom Label' )
    );

    return $schedules;
}
add_filter( 'cron_schedules', 'auto_post_job_function_own' );

if ( ! wp_next_scheduled( 'auto_post_job_function_hook' ) ) {
    wp_schedule_event( current_time( 'timestamp' ), 'post-change-24-hour', 'auto_post_job_function_hook' );
}

add_action('auto_post_job_function_hook', 'auto_post_job_function');


function auto_post_job_function() {
$args = array(
    'post_type' => 'post',
    'orderby'   => 'rand',
    'posts_per_page' => 1,
    );

$the_query = new WP_Query( $args );

if ( $the_query->have_posts() ) {

$string .= '<ul>';
    while ( $the_query->have_posts() ) {
        $the_query->the_post();
        $string .= '<li><a href="'. get_permalink() .'">'. get_the_title() .'</a></li>';
    }
    $string .= '</ul>';
    /* Restore original Post Data */
    wp_reset_postdata();
} else {

$string .= 'no posts found';
}

return $string;

};


add_shortcode( 'rand_post', 'auto_post_job_function' );