However, "Jussumguy" has alerted me to a Norwegian news report about the opera house exercise conducted by Oslo police, and it didn't take place exactly two days before the bombing. It was more like two days, four months, and a year. The story is dated March 17, 2010.
Now, to be fair, this could have been an accident. Watson posted a link to a translation of the Norwegian article, and the translation does not bear the original publication date. But if you were about to broadcast an already tenuous theory to the world, wouldn't you, I dunno, look at the original article?