Which planet has a moon that orbits at one revolution per <2 seconds

A few years ago I was on a mission to see all of the planets with my wobbly little telescope.
One night my uncle was with me when I was setting up my telescope. It was fall because I remember I had to acclimate my lenses and mirror to the cold. I printed out a swath of the southern sky from a star chart program that I downloaded. It showed that Jupiter could be found in the southern sky. I did find a planet, but it wasn't where Jupiter was supposed to be.
It was large and whitish-yellow. It had a black spot that made revolutions around the planet really fast. Close to one revolution per second. And I had to adjust my telescope to keep it in view a lot more often than any other planet I tried to follow. I still thought it was Jupiter, and I told my uncle that thing orbiting around it was the Great Red Spot. The next day I researched it and found out that I entered in the wrong date in the star chart, so I don't know which planet we were looking at. And I also found out that the Great Red Spot is a perpetual storm that slinks around the atmosphere of the Jupiter, not a fast orbiting moon...

If I had to guess: the wobbly little telescope had dust on the eyepiece and as it wobbled one would see a black spot moving across the disk of Jupiter, which may or may not have been in proper focus. This would probably look like something circling around. You probably DID find Jupiter as it is the brightest object in the sky (with the exception of Venus).

Even a bright star if out of focus will present as a large illuminated disk. It's difficult to say anything about the color because that too would change depending on how high the object was and precisely what it was you were looking at. A dusty instrument will present a different image than one that is regularly clean. In cold weather dew can form on the lenses and that will make a blurry, more diffiuse image.

On any given night there are many thousands of people looking at Jupiter and other planets in fairly high end instruments costing multiple thousands of dollars. On these instruments the eyepieces are generally cleaned regularly and the mounts are very steady. Some of these people are doing astrophotography.