You might be able to do something like this automatically on Linux at least. You can have a job that asks the X server what the title of the focus window is, which in the case of a browser will include the name of the active tab. In the case of a terminal, your prompt_command can set the tab or window title which would also get caught. Emacs can set its own frame title if you want that too. Etc. etc.

I suspect Hammerspoon on OSX could so something similar.

Pretty sure something like this exists for X11. If not, it would only be a few lines of shell code calling out to xlsclients, xwininfo, etc.

Think the same. The idea behind it isn't that bad though, the time interval could be configurable.

It makes me wonder if you could use a body camera and some machine learning to guess what the user is doing and then just provide a log to the user of their daily time spend. You could even break it down by minute. With a corresponding app on their PC and phone, you could turn "Phone time" into a description of what exactly they were doing on the phone.

You can change the time length.

Totally agree with that.