how long it takes before I can consider it mine
Ok, I checked it for you. Never is it going to be yours. You could claim the ownership of a movable property after 3 years but only on condition you don`t know the owner. If you do, you can`t claim it. Google the phrase Zasiedzenia rzeczy ruchomej (ruchomości).
When I mentioned 20 years in my first reply, it was correct but only in reference to real estate properties.