public function setTimeRange(DateTimeInterface $start = null, DateTimeInterface $end = null)
    {
        if (!$start) {
            $start = new DateTimeImmutable(Settings::$minDate);
        }
        if (!$end) {
            $end = new DateTimeImmutable(Settings::$maxDate);
        }
        $this->start = $start;
        $this->end = $end;
    }