You do not understand. Maybe use a different translator.
You claimed to be able to limit the time frame something can be downloaded after purchase.
Do you think is better to set a product for unlimited download after purchasing or set a limited number of time they can download it?
Actually I use to set "unlimited"
Three people, including the site admin, told you, this should not be possible. So what are you talking about? Do you read a translated version of the itch user interface? What option in the project makes you think you can limit the downloads after purchase?