Windows Services for desktop application in c#

You can, but also you can use the service which already exists, called Windows Task Scheduler, see:
http://en.wikipedia.org/wiki/Task_Scheduler[^],
http://msdn.microsoft.com/en-us/library/aa383614.aspx[^],
http://msdn.microsoft.com/en-us/library/aa384006%28v=VS.85%29.aspx[^].

See the last link above for use of the Windows Task Scheduler. You can use its API in your program using Task Scheduler Managed Wrapper, see http://taskscheduler.codeplex.com/[^].

But if can be even simpler. You can use Windows Task Scheduler using Windows utilities AT.EXE or SchTasks.EXE, see:
http://en.wikipedia.org/wiki/At_(Windows)[^],
http://technet.microsoft.com/en-us/library/bb490866.aspx[^],
http://en.wikipedia.org/wiki/Schtasks[^],
http://msdn.microsoft.com/en-us/library/windows/desktop/bb736357%28v=vs.85%29.aspx[^].

—SA