While making Purchase Order for counter-party, you have two option to enter delivery date.
In "Primary Document Details"
In "Item Section" for every item.
[A] In "Primary Document detail" the delivery date present here is the last date of delivery of an item from the list. It is by default delivery date for all the items until you specifically change the delivery date for an item in the list.
[B] In "Item Section" for every item we have option to change the delivery date from default to any other. This delivery date is available for every item in the list.
Note: The final delivery date for a PO is the date on which the last delivery is to be made.
Keywords: Multiple delivery date, Delivery Date, Item level delivery date, Final delivery date.