task.cs

void Main()
{
    //If the calling context is important (for example in GUI applications)
    //you'd might want to save the Synchronization Context 
    //for example: context = SynchronizationContext.Current 
    //and use if in the lambda below e.g. s => context.Post(s => this.Close(), null)

    var timer = new System.Threading.Timer(
                s => this.Close(), null, CalcMsToHour(23, 00, 00), Timeout.Infinite);
}

int CalcMsToHour(int hour, int minute, int second)
{
    var now = DateTime.Now;
    var due = new DateTime(now.Year, now.Month, now.Day, hour, minute, second);
    if (now > due)
        due.AddDays(1);
    var ms =  (due - now).TotalMilliseconds;
    return (int)ms;
}