Just over the course of an evening, it is often easy to detect changes in both Jupiter's surface features and in the positions of its moons. This evening when I began setting up the telescope, the red spot was at Jupiter's left edge. Now, a few hours later, it is past the center of the planet as we see it, moving to the right as Jupiter rotates. Jupiter completes one rotation in just about 10 hours.
Also earlier this evening, Io was crossing in front of Jupiter's disk and was casting a shadow on the planet. Now the shadow has left the disk and the separation between Io and Jupiter (as seen from our perspective on Earth) is getting greater with each passing minute.