Block dates let you close off specific dates so customers cannot select them for delivery or in-store pickup - useful for public holidays, days you are closed, or dates you simply cannot fulfil orders.
Go to Dashboard > Settings > Delivery Options > Blocked Delivery Dates.
Once blocked, that date simply will not appear as a selectable option for customers at checkout.
If you need to block every Saturday and Sunday rather than one-off dates, see the Block all Saturdays and Sundays article instead.