[C#]計算倒數一天

private double MillisecondsToNextTargetTime(TimeSpan targetTime)
{
        DateTime dt = DateTime.Today.Add(targetTime);
        if (DateTime.Now > dt)
        {
                dt = dt.AddDays(1); // we're already past todays target time; set it up for tomorrow
        }

        Console.WriteLine("Next run at: " + dt.ToString());
        return dt.Subtract(DateTime.Now).TotalMilliseconds;
}