Is it permissible to work in the field of on-demand T-shirt printing by creating a design and selling it, while providing details about printing and shipping times on a separate page from the main purchase page?

The aforementioned transaction is permissible, as it falls under what jurists call "Istisna'" (manufacturing contract). The Islamic Fiqh Academy has clarified that a specified term is a condition for it. Specifying the required period for preparing the product as "from two to seven days" means that seven days is the binding maximum limit, and anything before that is non-binding.