The filter is hardcoded and therefore cannot be altered now. When you inject the `DateTimeFormatter` filter via `__construct`, it is possible to use your own filter and the dependencies are much clearer. An example of this can be found in [SerializableStrategy::__construct](https://github.com/zendframework/zf2/blob/master/library/Zend/Stdlib/Hydrator/Strategy/SerializableStrategy.php#L33).