Why is it 20 minutes? It's just because I was arriving here late and this art museum was about to close in 20 minutes... I finally paid the ticket to quickly have a look of this museum, mainly because this museum is relatively far from the city centre. There's two main part in this museum, a sculpture park outside and an art gallery inside. So I decided to spend 10 minutes outdoor and another 10 minutes inside.
The ticket was 120 SEK for an adult. I simply thought that was a bit overpriced for a 20-minute visit... but you might find it a lot worthy if you could spend more time here though. However, I think this museum is quite small, I literally saw everything at the end. (It's probably because I was running out of time so I tried to see everything as quickly as possible.) Therefore, I assume you'll only need to spend an hour maximum here, or more if you want to enjoy your day in the park especially for the beautiful river view.
I was in a hurry and I didn't even have time to read the statement on the wall or so, so I have to say that I don't really know what this gallery is presenting at the moment... it could be a temporary exhibition but what I saw inside were something about Chinese culture and its embroidery art. There's not much to see though so I would say it would be a lot better if the entrance fee is lower.