HI Jack Delivery and welcome

It's very easy to do. First grab a copy of the "Syntax" list
from here..
http://forum.thegamecreators.com/?m=forum_view&t=180924&b=23 Helps a lot! Also look thru
the "Official Community Guide" in your Doc's folder for further help.
What you want to do is use a timer after your sound starts playing, "etimerstart" next you would use "etimergreater=20000"
the timer is in millisec's so 20sec's would be "20000"
When the timer expirers use the action "win" to end the level/game.
Try to make the script yourself, you might be surprised how easy it is. Come back if you need more help.
best
My games never have bugs. They just develop random features..