You can set a minimum delivery period in hours, which will be taken into consideration before showing the earliest available delivery date or time slot to your customers. This can be done under the "Minimum Delivery time (in hours)" field under the General Settings -> Date Settings tab in the Order Delivery Date on the admin side. Minutes will be accepted in the decimal format like for 30 Minutes you can use 0.50.


If you want that Wednesday should be available until 6 PM on Monday and Thursday should be available until 6 PM on Tuesday and so on, then you can set Minimum Delivery Time to 54 hours( 24 hours * 2 days + ( 24 – 18 hours ) ). 

Minimum Delivery Time can be set as 24 * number of days which needs to be disabled + the remaining hours of the current day.