public function get_time_left_display($attempt, $timenow) {
        $timeleft = false;
        foreach ($this->rules as $rule) {
            $ruletimeleft = $rule->time_left_display($attempt, $timenow);
            if ($ruletimeleft !== false && ($timeleft === false || $ruletimeleft < $timeleft)) {
                $timeleft = $ruletimeleft;
            }
        }
        return $timeleft;
    }