Linux Timer会在到期前触发吗？

Question

我们的游戏必须在每天24:00:00进行每日更新，代码如下：

Timer nextDayTimer(boost::asio::io_service& ios) {
    time_t now = time(NULL);
    struct tm tm = {0};
    localtime_r(&now, &tm);
    tm.tm_hour = 0;
    tm.tm_min = 0;
    tm.tm_sec = 0;

    time_t next = mktime(&tm);
    if (next <= now) {
      tm.tm_mday++;
      next = mktime(&tm);
    }

    Timer timer = Timer(new boost::asio::deadline_timer(ios));
    int diff = (int) (diffTime(next, now) * 1000.0);
    timer->expires_from_now(boost::posix_time::milliseconds(diff));
    return timer;
}

然后在达到计时器到期的时间进行每日更新。然后再次致电nextDayTimer;

然而，我发现它有一些问题，它偶尔会在24:00:00进行两次每日更新，这会导致什么原因？