The Pre-order Now app ensures that we do not disturb the elements of your website from loading or slowing them down as we understand they may be a priority for you. That being a reason, we wait for the website to finish loading first. If your website has a lot of failing scripts or takes a long time to load, it can take a long time to load.
To resolve this, we recommend you speak to a developer and ask him to speed up your website, or you can try doing it yourself by installing/adding a fresh theme. Both of these should resolve your issue and you'll notice that the Pre-order Now app is snappy! If you still face any issues, please contact the support team and we'd be more than happy to help you out!