Second hands won’t rotate on dim as far as I’m aware. I’m not sure what would happen if you tried alternating a minute or hour hand speed though. As for the speed at which they move in the creator depends on the device you are using the creator on. Things tend to run slower on the creator due to the browser in my experience. My phone runs very slow depending on how much is going on in the face but still runs. I often have to sync to my watch often to see how it really looks when creating animations on my phone. My pc runs much faster/smoother and has a more accurate depiction of what it will look like on the watch.
I believe that in dim mode, faces only update once every minute, meaning animation is basically impossible. I could be wrong, but I think that’s the case.