Once you claim a gift to your Guusto account it never expires. It will reside in your Guusto account until you are ready to redeem for a merchant gift card. That said, some senders put claim periods to ensure they only pay for gifts that are added to an account. To avoid your gift expiring - add it to your Guusto account as soon as you receive it.
One of our only gifts with an expiry date is Prepaid Mastercards - they expire six months after the redemption date.