The Expected delivery date can be configured to give a more accurate expected delivery date. This works on what is the 'base date' for the calculation and also how long it is expected for the goods to be shipped to a location. These settings can be set using the delivery settings window and setting the shipping lags.
The base date is can be one of the following using the shipping lag type
- The expected date
- The invoice Date
- In addition to ship date
You can then apply a shipping lag in days using the shipping lag field. Note the shipping lag if forward in days for the invoice date type, and backwards in days for if using the expected delivery date.
Also the In addition to ship date is applied to the ship date that comes from the ERP while the other 2 are related to the way the order is imported
See the article on Defaulting the Order Date for more information about setting the base date