private function getFormattedTimestamp($dateTime)
    {
        if(!$dateTime instanceof DateTime) {
            $dateTime = new DateTime($dateTime);
        }
        return $dateTime->format(DATE_ISO8601);
    }
private function getFormattedTimestamp($dateTime)
    {
        if(!$dateTime instanceof DateTime) {
            $dateTime = new DateTime($dateTime);
        }
        return $dateTime->format(DATE_ISO8601);
    }
Returns a ISO 8601 formatted string from a DateTime instance.
@param DateTime|string $dateTime
@return string