Passport control may take a while. On my last visit the regular passport line got bogged down with a flight to a country I shall not name that seems to have an inordinate number of visa issues. At least 5 times line got stopped, the person had a significant problem, commanding officers were called (I think one person was taken away somewhere). If you are unlycky enough to hit something like that - passport control will take forever.

OTOH while most seem to prefer Copenhagen, I always take a train the other way to Malmo. The bridge view is pretty neat if the weather permits, the town is compact and friendly and the food is better.

Not much to do near OSL - it's too far from the town. That green wall inside the terminal is neat.