add_filter('relevanssi_excerpt_content', 'custom_fields_to_excerpts', 10, 2);

function custom_fields_to_excerpts($content, $post) {
    $image_id = get_post_thumbnail_id();
    $image    = wp_get_attachment_metadata( $image_id);
    $image_meta = $image['image_meta'];

    if ($image_meta) {
      foreach($image_meta as $image_meta) {

         $date_shoot = date('d-m-Y', $image_metadata['created_timestamp']);
         $content .= " " . $date_shoot;
	   }

    return $content;

  }
}