Download posible after x days of completion

-- url of the page with the problem -- : www.air-learning.nl
-- HikaShop version -- : 2.2.2
-- Joomla version -- : 3.2
-- PHP version -- : 5.3.10-1ubuntu3.8

I use Hikashop in combination with joomdle. In this everythink works fine and happy with the Hikashop as product.
In the current setup when a customer buy's his product he automatic enrol into the course. Seperate from that i is it also posible to download the course on PDF.

Now i want to create that the user can only download the course after a x days after completion of the purchase.
This is not something that is build in the standard configuration of Hikashop but my question is this simple to create?

If you're a developer you can create a hikashop plugin and implement the onBeforeDownloadFile(&$filename, &$do, &$file) trigger to authorize or not the download of the file.