If there was such functionality what would you expect it to do exactly? Sales order represents certain commitment. Customer commits to buying goods and seller commits to selling them. If there is a specific 'deliver by' date then it is entered in the sales order and ATP runs that tells you and the customer whether this date can be met. If this date doesn't work for the customer, the order may be rejected. If something goes wrong before the delivery (e.g. vendor fails to deliver, quality issue, etc.) then I guess you'd need to provide the customer with an update. I'm not an expert on this but there also might be some mechanism in the delivery to prevent late deliveries to the customer.
Quotation and contract are the documents with expiration date, but I just don't really see how a PO expiration date would blend into a regular sales order process...