That seems like a lot of work. The last thing I want to do when applying for a job is open up some random code and hack it. I have many other things I'd rather do, like sleeping or working on some code I care about. Google doesn't do it, Amazon doesn't do it, so if that's who you're competing against for developers, why would you do it?
Also, if you can't be bothered to spend 30 minutes proving that you can code, how much do you really want to work there? The only time I've done one of these challenges was for a company that I was really excited about working for.