I have a php script that I am releasing free and I want to setup a demo of it on my website. However, I would like for the demo to reset every 4 hours.

Here is how I would prefer the reset to work. Everything will be auto deleted from the database and then the cron will access a specified .sql file to restore the database from. For example it will take the file "http://www.mywebsite.com/backup.sql"

How would I set something like this up? I have been searching for code or a script that does this and can't find anything.

I'm not sure if there is a special script to do that but why don't you create the script your self? you can run your script by cron every 4 hours so it reset every thing to default. (actually I think I didn't realized your exact problem!)

I'm always puzzled why so many think that a demo has to reset at a given time, and then play about with cron jobs or schedules.

Just check if it needs to reset when a user starts the application and reset it then.

hmmm, good point chrishirst,. Also, I might even have a database table to serve as a log to record how much usage it is getting so I can review how/where they go and how they use it.

Try using "TRUNCATE table_name" to remove all info from your DB (better than purging your DDL and rebuilding).

Try using the empty-table button manually
After all... it's just a demo. Wouldnt make that too advanced IMHO
Crons I use only for the hardcore hardcore production-process only. After testing everyting... manually.