Screentime by fyrot

The Screentime extension works exactly how you'd expect it to - it provides useful stats about the time you spend on websites you visit!

As of now:
-the 'stats' page: lists total time spent on your top five most viewed sites + total time on the current site.
-the 'settings' page: has preferences on how information is presented that you can tweak to your liking.

Found here on GitHub