Magento sets the backend type for all user-created date attributes as datetime. This is different from created_at and updated_at, which has the backend type of static. The Algolia extension defaults to how Magento formats dates on the backend.
However, you can use the algolia_after_create_product_object method to modify the format of that attribute once the record has been created in the Algolia dashboard. You can find more information about the method in our documentation regarding custom backend events for Magento here.