You could probably utilize the post object query filter and adjust it to look for a post_status of future in addition to the default publish.
https://www.advancedcustomfields.com/resources/acf-fields-post_object-query/
So it would be something like:
add_filter('acf/fields/post_object/query', 'my_acf_fields_post_object_query', 10, 3);
function my_acf_fields_post_object_query( $args, $field, $post_id ) {
// Show scheduled posts, as well
$args['post_status'] = array('publish','future');
return $args;
}