1. Good move to protect yourself as a developer and making the app easily available <i>outside</i> the App Store.
2. Consider supporting older macOS versions.
3. Have a look at <a href="https://workrave.org/" rel="nofollow">https://workrave.org/</a> and <a href="https://www.dejal.com/timeout/" rel="nofollow">https://www.dejal.com/timeout/</a> for additional feature consideration (competition research). (Tip: Workrave is better, even if TimeOut looks nicer - focus more on that).
Very cool idea. This would also be kind of cool to have a timer that would remind you to look at something in the distance every 5 to 10 minutes to keep your focus range exercise while using computer.
I don't see a LICENSE file. Do you intend to choose a license?<p><a href="https://choosealicense.com/" rel="nofollow">https://choosealicense.com/</a>