How do I load an mp3 after this javascript is complete?

I've tried to figure this out for an hour now, but it's pretty obvious I don't know Javascript.
Basically this is a countdown script and after it finishes I'd like it to load an mp3 or a page.
It even says where I can add the code, but I'm just not sure what to do. All help is appreciated!
Here's the code:
You can see where it says

/* HERE YOU CAN ADD TO EXECUTE A JavaScript FUNCTION WHEN COUNTDOWN TIMER REACH TO 0 */
Click to expand…

I figure I should be able to do this.

Code (text):

<form>…

How do I load an mp3 after this javascript is complete?

See original post by wallarookiller