Help with countdown with drag-and-drop interaction

I'm creating some drag-and-drop quiz questions, and I want to have a countdown element playing throughout. The way I envision this working is that the countdown timer continues to count down to zero, if the user drags the correct response onto the target the Correct layer will show and the slide will advance to the next question when the user clicks "continue," and if the user drags the incorrect option onto the target the Incorrect layer will show, and the slide will advance to the next question when the user clicks "continue."

The countdown timer is set up as a series of layers that are set to change using the timeline.

For some reason I can't get this to work correctly. I've tried changing the slide layer properties, and that isn't seeming to work.

I'm attaching a file of the slide I'm using so that you can see how I have it set up.

Thanks for any input!