public function getTimeFromConfig($config)
    {
        $now = $this->date;
        $period = $this->processConfig($config);

        $sub = $this->processPeriod($period);

        if (isset($sub)) {
            $period = $now->sub(1, $sub);
        }

        return $period->toString(\Zend_Date::ISO_8601);
    }