1. Enable PHP on your machine by opening "/etc/apache2/httpd.conf" in a text editor and uncommenting the following line (remove the leading "#"): "#LoadModule php5_module libexec/apache2/libphp5.so" or install
MAMP to run Apache and PHP locally (much easier).
2. In your System Preferences, go to the "Sharing" tab and turn on "Web Sharing."
3. Download
this file (option click on the link if it opens in a browser window), delete the ".txt" suffix, and place it in the "Sites" directory in your User folder.
4. Open a web browser and navigate to
http://localhost/delaywall.php?file=somefilename.mp3&time=650000, where "somefilename.mp3" is the name of the file (also in the Sites directory) that you want to delay (it can be a .mp3, .mpg, a .pdf, a .zip, a .mov, an .avi, a .dmg) and the number following "time=" is the approximate number of seconds you want the download to take. Browsers behave slightly differently and processor speeds make a difference, so your mileage may vary.