I would think that httpwebwitch's last method (with an incrementing counter/id in a text file) is perhaps the better solution. This would also avoid the situation that if (for some reason) your script didn't run for several minutes no products would be missed. Also, if the script did run more than once in any one minute you wouldn't update the same product twice, unless you checked for this.
Just going back to your original query about linking each minute of that week to a product... I don't think you need to even bother about weeks, as long as you have decided that it's 1 product per minute and it should loop continuously. Using httpwebwitch's modulus idea...
$product_number = (time() / 60) % $number_of_products;
If $number_of_products is 10,000 then $product_number will return a number between 0 and 9,999 based on the current time in minutes. This, however, will loop marginally shorter than 1 week if that is the major factor.