Depending on the test center, you might experience lag between passages (when you press the "Next" button). On my MCAT, there was a significant lag (5 seconds) between pages and it was incredibly annoying and worrisome at first but I just got used to it. I think I also lost a few seconds every time it did this (but it was only 2-3 minutes total or something, probably). So be mentally prepared for such a thing, if it were to happen.