WP Query ordering on a meta field for posts with a date in the future not ordering by datetime

The docs are a little vague in this area, but it should be possible to define your ordering value more succinctly:

   $args = array(
    'post_type' => 'post',
    'post_status' => 'publish',
    'posts_per_page' => 5, 
    'category__in' => $postCategories,
    'meta_query' => array(
        array(
            'key' => 'ordering_date',
            'value' => date("Y-m-d H:i:s"),
            'compare' => '>=',
            'type' => 'DATETIME',
        ),
    ),
    'order'     => 'ASC',
    'orderby'  => 'meta_value_datetime',
    'meta_key' => 'ordering_date',
    );