Yes, but Norway controls the sluice gates and has an idea of when demand is high or low. I guess you could argue that their generation capacity is limited and during peak they simply can't offer anymore, but other than that, Norway can totally ramp down production at night.
The demand for electricity in Europe is so high that Norway could sell every watt-hour if the DC links and HV AC backbone had enough capacity. Essentially the only thing preventing Norwegian electricity prices rising to European levels is the lack of capacity in the backbone HV system not the ability to control the generators.
