Slide layer navigation issue

Having an issue with slide layers... I want the learner to listen to the base layer audio, then have the learner listen to audio on the slide layer. However, once there, how can I force the learner to listen to the entire audio file on the slide layer before they press the "Next" button on the navigation bar and progress to the next slide? Is there a way to "hide" the "Next" button until the audio on the slide layer finishes?

Suggestions? Thanks in advance!

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