Many stores require mandatory delivery date and time, they also want delivery date and time to be validated ,on their operating hours time like order placed after 4pm cannot be delivered on the same day.
This vqmod based extension does the same.It facilitate user to bar special days like Christmas etc and set operating hours so that delivery date could not be made after operating hours.
It makes selecting delivery date and delivery time mandatory. It lets you set server offset so that any discrepancy between your server and your operating hours is ruled out.
It is Vqmod based no core files have been touched or changed
Selected date is visible on order details page .

If you are looking for only delivery date and not delivery date with time you should buy this extension.

http://www.opencart.com/index.php?route=extension/extension/info&token=75fb110ffac16b88abce020bc1078763&extension_id=12069
If you want slot based extension check this wonderful extension
http://www.opencart.com/index.php?route=extension/extension/info&extension_id=24979

Compatible with journal2.7 theme since opencart 2.x.x version

Please note that it works with opencart default checkout system , other custom checkout extensions like onecheckout, quickcheckout etc won't be compatible with this.To make that compatible extra may be charged.
Extension is made by shambhal networks who holds the highest opencart reviews on freelancer.com
For further queries you can contact me at shambhalnetworks@gmail.com