How long does it take to cook baked potatoes at 200 degrees?

Cooks illustrated has a great recipe for salt baked potatoes. They cook on a bed of salt and they are to die for!

200C is about 425F, and it depends if the potato is room temp or from cold storage . And, what size? Count on a hour - I continually test by sticking them with a knife to see how easy the blade goes in. Easy means done, hard means keep waiting. Simple as that.
I like to coat the skin with olive oil and prick and sprinkle with sea salt.

Are you referring to 200 degrees Celsius? I bake potatoes at 400 degree Fahrenheit for about 60 minutes; 400F is roughly equivalent to 200C.