To be honest my idea would be to just lose the service and change to a scheduled task. I have many scripts running now that basically do what you describe, but run as scheduled tasks and not as services, and they seem to work just fine. Unless there is a really good reason to run as a service (ive yet to hear one in my job but....) then setting up a repeating scheduled task (not using the at command but the scheduled tasks facility available through the control panel) should do you nicely.

Beyond that anything I could offer would be completely off the top of my head conjecture and unlikely to be useful.
:-(
Sorry.