Windows Service that runs Periodically
I typically use a Timer, then stop it when the process starts to run.
Here's an article that explains how to do it.
This is not a very good idea, since you lock your thread for the full period of "SleepTimeHours" and you won't be able to even stop the service in the meantime.
You could either make this service so that it would sleep for e.g. 5 seconds and then check whether it's time to get back to work, and if not, sleep another 5 seconds (that would give you the necessary responsiveness, if you need to stop the service).
OR: you might be better off just writing a console app that can be scheduled using the Windows "scheduled tasks" feature in order to be run every x hours. That way, you won't be blocking or using any system resource if your app isn't doing anything......
Marc