Have a look at the orderby parameters for WP_Query to see all of the valid values that can be.
If wpcf-start-time is a meta key, then orderby should be meta_value, which will also require you set a meta_key argument to tell WP what meta key you want to order on-
} elseif ($q->is_post_type_archive('cif-events')) {
$q->set('orderby', 'meta_value');
$q->set('meta_key', 'wpcf-start-time');
$q->set('order', 'ASC');
$q->set('posts_per_page', 300);
}