I have a service that user can configure to run during \"off-peak\" hours. They have the ability to set the time frame that the service can run.
For Example:
I'm assuming you are saving the start and end times in the applications configuration file, so all you basically have to do is have your application set a flag to "on" when the "start time" occurs and set it to "off" when the stop time occurs.
That way you don't have to be constantly checking if "now" is "between start and end" times.