Thanks Jodi! I'll include the download in the Feedback section, it might be easier to explain if you can see the method.
Off the slide I have a circle with two motion paths (Down and Up). I set up a number variable (Glow) to add 1 each time the Down motion path completes. The change in variable then triggers the "Glow" layer appear.
The Glow layer has the exact same icon but with a custom shadow effect applied to it. I have that layer set to hide when the timeline ends (I adjusted the timeline and the motion paths to my liking). I also added a fade in and face out effect on the glowing icon so that it was a little more of a smooth transition.
It's very possible that I over-complicated it a bit but I've used this method a few times and I really like it. I can't take credit for it though, I found a YouTube video walking through these steps ages ago. I've never found it again but it was extremely helpful. Let me know if you have any questions!