Log software usage time on Mac OS 9 (Oct. 1999)
What I would do is install Mac OS X 10.5 Leopard, on a PowerPC PowerMac and then install OS 9 into the Classic Environment, and have your user run their application there. You can still find new and full retail versions of Leopard with the licensing intact, and online support is still available.

Then, I'd use your bash script (with a possibly needed slight modification to track use of the entire Classic Environment rather than the specific application). ;-)