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
Scroll down to the Shipping section and click Enable date picker
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.