Correct, but the time you can stay is surprisingly generous in Oslo, between 3 and 24 hours, depending on location. I used to dread driving to Oslo, but after I discovered that the municipality had repurposed an old bunker to fit hundreads of chargers/parking spost dead in the middle of town, I visit with gleeful joy :P
I see on that map, that on my last visit to Oslo I could have parked 20m from my hotel entrance for €10 over night, instead of parking in the garage 50m further away for €120. Didn't really need to charge, so just went for a normal spot.
This usually means you can't stay for a particularly long time.