You can use the formula below in the Calculated Fields section of the Data Settings to calculate the number of days from when an order was placed and when the shipment was delivered to the customer:

days_diff(to_datetime({{ fulfillments.events.last_delivered_event.happened_at }}), to_datetime({{ created_at }}))

Note that the "fulfillment events" data, which contains the date of when the package was delivered, may not exist for all shipping carriers.