Functionally, you will require the following.
1. Maintain the gift card expiry period(The number of days from issuance when the card will expire). You can create a new field in Commerce parameters or use the Commerce configuration parameters.
2. Add a new field called expiry date to the gift card table.
3. Modify the issue gift card RTS call to define an expiry date based on step 1 at the time of card creation.
4. Modify the redeem gift card RTS call to validate the expiry date during redemption.