When testing various ideas, I often need a large amount or records. While Filemaker creates them, I want to do something else, but still be updated on how far it is in doing it. However, the trivial idea illustrated below can be used in other (developer) situations.
Simply put, while the script is running, a Filemaker window will move from left to right; when it reaches the left side of the screen, your script is done. Your upper screen real estate becomes a progress bar.
The window will move even if Filemaker is not the front application; right now it's moving behind my browser window and I can see it "at work" while I type this message.
You can adapt this in various ways (like using the front window instead of creating a new one) etc.
Have fun: run the only script available, to begin with. Tweak as needed.