https://www.cnet.com/news/new-amazon-day-shipping-option-lets-you-pick-the-day-you-get-deliveries/

For example, if you pick Thursday, all the stuff you bought during the week, and select at checkout to arrive on your "Amazon Day," will be waiting on your doorstep when Thursday comes around.

Prime members who join the program will still be able to select their regular one-day, two-day and no-rush shipping options (if they're available) for every order. Most items that are available for two-day deliveries will get the new Amazon Day option.