In RACER there are two kinds of due dates: The date entered by the lending library when they action Shipped, which is meant for the borrowing library; and the "Local Due Date" entered by the borrowing library when they action Received, which is meant for the patron. (By default the Local Due Date field on the Received screen displays the library due date, unless edited by borrowing library staff.)
The library due date appears only on the staff side, in the Additional Service Details of the request. The local due date is visible both for staff and for patrons in RACER. The patron in ZPortal sees the local due date in the Date Due field of the request when s/he checks My Requests. The local due date also appears on the Received Book Band.
Here is an example of a request where the lending library indicated a due date of June 7 and the borrowing library entered a Local Due Date of May 31:
In VDX (staff side):
In ZPortal (patron side) and on bookband: