Using the notification tool

Of course you can develop any kind of application using timer events with time period calculated based on the initial real time taken from the system, but, to keep it running at all times, you would need to develop a Windows Service. You can add any kind of timing to your service just because you can use a timer and System.DateTime structure, see:
http://msdn.microsoft.com/en-us/library/system.timers.timer.aspx[^],
http://msdn.microsoft.com/en-us/library/system.threading.timer.aspx[^],
http://msdn.microsoft.com/en-us/library/system.datetime.aspx[^].

But why? I want to give a different advice. Don't you think you would better off using existing service which is designed to support really complex schedules? It is already bundled with Windows and enabled; you can use it on different levels. It is called Window Task Scheduler, see http://en.wikipedia.org/wiki/Windows_Task_Scheduler[^].

First, you can schedule events using command-line utilities AT.EXE or CSHTASKS.EXE (which is replacing AT.EXE), see:
http://en.wikipedia.org/wiki/At_%28Windows%29[^],
http://en.wikipedia.org/wiki/Schtasks[^],
http://technet.microsoft.com/en-us/library/bb490866.aspx[^],
http://msdn.microsoft.com/en-us/library/windows/desktop/bb736357%28v=vs.85%29.aspx[^].

And you also can use Window Task Scheduler API, please see:
http://msdn.microsoft.com/en-us/library/windows/desktop/aa383614%28v=vs.85%29.aspx[^],
http://msdn.microsoft.com/en-us/library/windows/desktop/aa383608%28v=vs.85%29.aspx[^].

To see how can you use it with .NET, see this CodeProject article: A New Task Scheduler Class Library for .NET[^].

—SA