I’ve had to write code similar to this before (though it was with a program and not with mp3s). What my boss decided on (was cheaper than paying me to do it the other way, which I’ll explain in a sec) was getting me to write a script that takes his program from a secure location (not in the wwwroot) and copies it to a random name in the downloads folder, linking to it on the page. If any of the timestamps on these programs are more than 15 minutes old (they would take about 5 mins to dl at 56.6 so 15 mins is the time I chose) they get deleted.
The other way to do it (if you are using apache) is with .htaccess. I don’t think it will take you too much more time, but for the life of me I couldn’t get it working properly, so I’ll refrain from giving bogus advice. Google for .htaccess and you’ll find stuff right away.