My bad - I was confusing two things together and have edited a bad reference out of my original post. Having cleared that missunderstanding, using CallInterval seems reliable enough.

Thank you for pointing me into the right direction. My Service now downloads file "errors.txt" and then in OnProcessInput method I call the following to delete "data.txt" from the same folder where "errors.txt" was downloaded from:

If ..Adapter.delete("data.txt", pInput.Attributes("FTPDir") ){  <log that deletion was successful> }

Exactly what I was looking for and worked.