If you would like to ask your customers to select a date for shipping before they checkout then follow the instructions below.
Click Settings from the main menu
Click on the Shipping option:
Scroll down to the Date picker section and click Enable:
Check the days of the week that you offer shipping
Please allow a couple of minutes for your changes to be updated within Shopify.
Now when your customers visit your shopping cart page and select Shipping they will be asked to choose a date before they can proceed to the checkout.