This plugin adds a delivery times section for backorders to WooCommerce Shipping settings to set a default value (number of days). It also adds a field to enter a number of days on the product at the inventory level (simple products or variations), fields accessible when backorders are authorized. It is thus possible to define a number of days different from the default one on the products. Finally, a text to be specified in the settings such as "available within 14 days" is displayed on the product page, the cart, and the order.
webaxones/wax-wc-product-delivery-time
Add a field to WooCommerce product to set an estimated delivery time in days
PHP