>This works, but make sure they spend the 2 hours in your office and not 12 hours at home solving a 2 hour problem..

Did you read the article?

That's what the article author is saying not to do, they prefer to see a well worked solution after you define a particular technology, showing they are adaptable and have thought it through properly.

Limiting them to your office, timeboxed, advantages people who spit out lines of code quickly, which is definitely not the right fit for a huge amount of coding positions, especially when you are emphasising logical choices and design decisions.