Date format in TYPO3 backend can be customized with::

    $GLOBALS['TYPO3_CONF_VARS']['SYS']['ddmmyy']
    $GLOBALS['TYPO3_CONF_VARS']['SYS']['hhmm']

Rendering is done by ``TYPO3\CMS\Backend\UtilityBackendUtility::datetime``

Example value::

    'ddmmyy' => 'Y-m-d',