We tried to order a product marked In Stock but the Order shows a long Estimated Delivery Time. Why?

If you place an order for a quantity more than 1, check the product availability in the Cart. For example, we have 5 pcs in stock and you order 6. The availability in the Cart switches from In Stock to Order when you change the Cart quantity to 6. The Order will show a long EDT (Estimated Delivery Time) for 6 pcs but a short EDT for 5 pcs.