Here is what the help says, basically the different dates are calculated depending on different setup parameters. You set some of the parameters in Warehouse set, outbound time, there are planning lead times on the item card, so if the item is not in stock it uses that to calculate the fastest you can get it from the vendor. So, it is a combination of a lot of differenct setup parameters, hope this helps.
Navision 4.0 help file information
The program will calculate the earliest possible date that an item on a sales order line can be shipped and/or delivered.
If the customer has requested a specific delivery date, the program calculates the date on which the items must be available to pick to allow delivery on this date.
If the customer does not request a specific delivery date, the program calculates the date on which the items can be delivered, starting from the date the items are available for picking.
Promising a Requested Delivery Date
When you enter a requested delivery date on the sales line, the program uses this date as the starting point for the following calculation:
Requested Delivery Date - Shipping Time = Planned Shipment Date
Planned Shipment Date - Outbound Whse. Handling Time= Shipment Date
The program checks if the items are available to pick on the shipment date.
If the items are available to pick on the shipment date, the process can continue.
If the items are not available to be picked on the shipment date, the stock-out warning appears.
Promising the Earliest Possible Delivery Date
If there is no requested delivery date on the sales line, or if the requested delivery date cannot be met, the program finds the earliest date that the items are available. It then enters this date in the Shipment Date field and calculates the date you plan to ship the items as well as the date they will be delivered to the customer, using the following formulas:
Shipment Date + Outbound Whse. Handling Time = Planned Shipment Date
Planned Shipment Date + Shipping Time = Planned Delivery Date