Summary
In Sage X3 the date written in the shipment journal STKSD is the date when the shipment is created.
Resolution
There’s no standard way to set the stock journal posting for a shipment to the validation date rather than the date it's created.
Any changes to the automatic journal STKSD from the IPTDAT would likely lead to issues with the stock movements and stock GL reconciliations. For that reason any changes to the journal wouldn’t be supported.