there is not going to be an automated way to do this, it will require some set up on your part.
probably the easiest way is to create a new column in your database to hold the date that a particular product should be the Product of the day.
you will need to set this in the database for each product.
then you can use a reordset to return the product that is set for today:
SELECT * FROM products WHERE DATE_FORMAT(podDate, '%Y-%m-%d') = DATE_FORMAT(now(),'%Y-%m-%d');