Your concept or idea should be developed enough to support a three minute presentation, but it is not necessary to have a working model to "demo" ... it's the idea that's important! There are three minutes for delivery and three minutes for discussion (or 6 minutes to use however you see fit...previous attendees highly recommend time for interaction, questions, etc.). The time limit is strict so if you take two and a half minutes to setup your laptop, you only get thirty seconds to present (the gong hath no mercy).
Official Website: http://www.barcamp.org/DemoCampVictoria