Transtions NOT TIED TO THE TIMELINE?

Hello there!

 I have a page where when learner hovers over a button, it will trigger an action to hide a already displayed layer. Is there any way to use an animation to fade the layer that does not depend on the timeline?  I can't seem to figure out how to get the layer to fade away. When I hover over a button, the layer hides but it seems very abrupt. There must be a way to do this, just don't know what it is.

Thanks!

KV