I have a post that contains a list of recent posts from another post type. These posts are added daily. I would like the thumbnail of the main, listing page to grab the featured image of the most recent post in the list.

I am (probably obviously) a total hack at programming. I started with the code below but wondering if it needs to happen when a new daily post is created? I am now just confused and hoping for some help. Thanks!

function set_custom_thumbnail( $post_8661, $thumbnail_id ) {
  $post_8661 = get_post(8661);
  $args = array(
    'post_type' => 'wakeup',
      'post_status' => 'publish',
      'posts_per_page' => 1
  );
  $new_query = new WP_Query( $args );
  if ($new_query->have_posts()) {
    while($new_query->have_posts()){
        $new_query->the_post();
        $thumbnail_id = the_post_thumbnail('thumbnail');
        }
      wp_reset_postdata();
    }
    return update_post_meta( $post_8661, '_thumbnail_id', $thumbnail_id );
}