It would be very useful, and imo logical, that the demo system should replay the previous day's data instead of random data, where today becomes the previous day after the regular trading day ends. Not sure how that would handle 24-hour markets, but some reasonable thing there is ok. It can't be worse than random data. This is not hard to do. Just use Etherea (or similar packet capture software)l to capture the packets, and then replay by pumping those into your demo system.