This is horrible: among other head-scratchers, author advocates "saving time" by blatantly cheating. A "clever (sic) rehearsed demo" that "covers up" the fact that you didn't actually write the application code you say you wrote isn't saving time, it's cheating. The point of a hackathon demo is to show how much progress you made towards an idea in a given amount of time, not to put on a smoke & mirrors show.