better fix for #5448 not using customized DateTime class

fixes #6263 and has no problem with PHP Bug:

> it is a PHP bug: https://bugs.php.net/bug.php?id=45543
> Fixed in this commit: php/php-src@22dba2f#diff-7b738accc3d60f74c259da18588ddc5dL2996
>
> Fixed in PHP >5.4.26 and >5.5.10. http://3v4l.org/mlZX7