Comment by throwway120385

This is exactly what I do. It's rare that someone is required to create something entirely from scratch. Most of what we do as developers is altering an existing system. I want to select for people who can figure out how to do that.

Also it completely eliminates the tool selection and test system portions of the exercise because I pick all of that stuff and make sure anything I don't care about is automated or is out of scope of the solution.

Done correctly you can usually get through it in less than an hour, leaving about 10 or 15 minutes for the candidate to ask me some questions.