Setup Custom Message on Checkout with Calendar

I have Hikashop Essentials and am trying to add a custom field to the checkout where customer can sepecify time and date for delivery. Is there a way to do this?

That can only be done with the Business edition by creating a custom field of the table "order" and of the type "date".
It will be displayed by the view "fields" of your checkout workflow so make sure that you have that view in your checkout workflow and that your custom field's front end option is turned on.