If you need to postdate a shipment to be sent at a later date you can change it by clicking on Ship Date on the Ship screen and selecting a new date. This can be done for up to 7 days in the future for USPS and FedEx, and up to 30 days the majority of other carriers.
If processing in the Batch screen, in the Edit panel on the right, check the box to edit the Shipment Date. Select the date you will ship and select Save changes.
It will display the ship date above the shipping service selected within the batch screen if it is postdated.