Can Premiere tell me how long was I working on a project? To measure active work time?

Past Peru Bob's useful comments, always checking with aescripts.com is a good thing. They have SO many plugins from all sorts of creators, that do many useful and amazing things.

I haven't used this and can't speak for its effectiveness, but this may be what you need:

https://timingapp.com/adobe-premiere-time-tracking#:~:text=How%20do%20I%20track%20time,your%20videos%20in%20Premiere%20Pro.

also here:

https://timeanalyticssoftware.com/billable-hours-tracker-software/