Spend a day or two in Oslo.

Is Oslo Citipass worth it? Semtember 16, I plan to fly from Stockholm and arrive Oslo at 10:45am and spend that day in Oslo. Next day, I plan to do one day Norway in a Nutshell (one way to Bergen, plan to buy ticket at the train station) which the train leaving Oslo at 8:00am. I need some advice..should I spend an extra day in Oslo?

Thanks for any advice.