Show estimated time delivery

Hi,

If you create a custom field of the table "order" via the menu Display>custom fields, you can configure the field value to be visible in the email notifications, the invoice, the order details page of the customer, etc. And you can enter its value when you edit the order in the backend.

Now I don't know where you want to display the time delivery or how you already are displaying it ? You could also display some text during the checkout saying that the delivery would take 3 days after the payment for example.