think\Model::autoWriteTimestamp PHP Method

    protected function autoWriteTimestamp($name)
    {
        if (isset($this->type[$name])) {
            $type = $this->type[$name];
            if (strpos($type, ':')) {
                list($type, $param) = explode(':', $type, 2);
            }
            switch ($type) {
                case 'datetime':
                case 'date':
                    $format = !empty($param) ? $param : $this->dateFormat;
                    $value = date($format, $_SERVER['REQUEST_TIME']);
                    break;
                case 'timestamp':
                case 'int':
                    $value = $_SERVER['REQUEST_TIME'];
                    break;
            }
        } elseif (is_string($this->autoWriteTimestamp) && in_array(strtolower($this->autoWriteTimestamp), ['datetime', 'date', 'timestamp'])) {
            $value = date($this->dateFormat, $_SERVER['REQUEST_TIME']);
        } else {
            $value = $_SERVER['REQUEST_TIME'];
        }
        return $value;
    }