How can I add a time limit for developer products?

I recently added a developer product to my game that allows players to upgrade their gameplay, and earn more perks. However, I have the product set up to be a one-time purchase, instead of a timed purchase. What I mean by that is, I want the player to be able to "subscribe" to the perks, and after one month, make the perks disappear. I am not quite sure how to make it expire after one month, and any help or resources would be greatly appreciated.

I apologize if this seems like a request, but I know how to create and handle developer products, but I am not sure how to implement a time limit for them so they will have to purchase it again to re-gain the perks.

EDIT: The subscription will be based on visits instead of time periods. Thanks to the people in the comments for the help.