How to Expire a Post Based on Meta Box custom field value

OK, I've got this working with some more research on this forum. Here's my code:

// expire exams on date field.
if (!wp_next_scheduled('expire_exams')){
  wp_schedule_event(time(), 'hourly', 'expire_exams'); // this can be hourly, twicedaily, or daily
}

add_action('expire_exams', 'expire_exams_function');

function expire_exams_function() {
    $today = date('Ymd');
    $args = array(
        'post_type' => array('exam'), // post types you want to check
        'posts_per_page' => -1 
    );
    $posts = get_posts($args);
    foreach($posts as $p){
        $expiredate = get_post_meta($p->ID, 'end_date', true ); // get the raw date from the db
        if ($expiredate) {
            if($expiredate < $today){
                $postdata = array(
                    'ID' => $p->ID,
                    'post_status' => 'draft'
                );
                wp_update_post($postdata);
            }
        }
    }
}

I then used the WP Crontrol plugin to get more visibilty over the cron job.