Hi staminka,
The listings displayed in your scrolling gallery don't necessarily change every 4 hours, but they certainly have the potential to.
The scrolling gallery is set to display 14 of your active listings at a time and is refreshed every 4 hours. Each time the store window refreshes, it is populated with another 14 of your current listings that are ending around the same time as the next auction of yours that is viewed. Also, when items that are displayed in your scrolling gallery end, they will be replaced with new items the next time the scrolling gallery refreshes.
-Mike