Looks nifty. Have you considered using Shell.AppUsage? It does a lot of this sort of tracking and more. Of course, you can't use it in its current state (you could parse the XML manually, actually, but bleh). I wrote a few patches to turn it into a real API: https://bugzilla.gnome.org/show_bug.cgi?id=673767

Thanks. I didn't know about AppUsage until the extension was mostly complete. When I looked at the XML it produced it provided weights instead of actual times (which I was primarily interested in) so I decided to continue with my GJS implementation. I'll take a look and see what's changed, it might be helpful for providing history of usage graphs.

Newer version approved -- this one not needed.