Why not immediately? Because I'm a happy user of ActivityWatch -- a fantastic similar tool, which, quoting the authors is " The best free and open-source automated time tracker. Cross-platform, extensible, privacy-focused."
I encourage you to check it out, if you haven't already. The pluggable and diverse watchers that AW uses are the true source of its power. It's under active development (donno why another comment claimed otherwise) and I've been using it on everything for 2 years now.
I can't wait to do a head between the two, and a writeup. I'm sure there are features that will "cross potentate" between the two projects
