You don't say if this is for a web setup, and if so, what web server.

For low performance, your authorization script can return a URL that points at your deliver script, and the delivery script can confirm that the request is not "too old", and if OK, deliver the content.

For high-performance, you can use mod_perl to handle the delivery URL that simply sets the request filename to the content during the TransHandler phase, provided the timestamp again is not too old, and otherwise returns a 404.