Car Covers come in two varieties, Custom Fit and Universal Fit.
Custom Fit covers are manufactured to fit your specific vehicle. To achieve this level of fit, these items are almost always made to order. The manufacturing process usually takes from 3 to 14 days. Once your cover is made, it is shipped direct to you from the factory, based on the shipping method you selected at the time of purchase. So, purchasing 1 Day Shipping will definitely get your order to you as quickly as possible, but it does not usually mean that you will receive it the next day.
Universal Fit covers have a generic shape that can fit more than one vehicle. The covers are quite often pre-cut and in stock. So paying for 1 Day Shipping will usually mean an overnight delivery (assuming of course that your order is received early enough in the business day).