I would do it as a view. This is basically a select statement where one result column is the ship date. You can add other relevant columns too. Any app with access to the database can then access the view the same way as ordinary tables.
If your table looked like:
create table orders(id INTEGER PRIMARY KEY AUTO_INCREMENT, order_date DATETIME);
and you always shipped 3 days after, you could use:
create view order_view as select id, order_date, order_date + INTERVAL 3 DAY as ship_date from orders;
The select statement can be made as complex as needed. Then, you just read
order_view in any application, as if it were an ordinary table.