public function getMinStartTime(string $listID = ''): ?int
    {
        $list = $this->getListData($listID);
        if (empty($list)) {
            return null;
        }
        $minStartTime = null;
        $hasTaskWithoutStartDate = false;
        foreach ($list as $taskListData) {
            if ($taskListData[0] === 1) { // version check
                if ($taskListData[1] === null) { // does not have start time
                    $hasTaskWithoutStartDate = true;
                } else { // has start time
                    if ($minStartTime === null || $taskListData[1] < $minStartTime) {
                        $minStartTime = $taskListData[1];
                    }
                }
            }
        }
        $currentTime = time();
        if ($minStartTime === null) {
            return $currentTime;
        }
        if ($hasTaskWithoutStartDate) {
            return $minStartTime < $currentTime ? $minStartTime : $currentTime;
        } else {
            return $minStartTime;
        }
    }