By allowing your gift cards to expire you will encourage your customers to use the gift cards in a timely fashion.
In Gift Up! you have a choice and you can change the default on the gift card settings page:
You are also able to edit individual gift cards to modify their specific expiry dates, for example to extend a date:
Note to our USA customers
We recommend not setting an expiry date due to federal law. Also, in some states it is required that you display an "issued on" date. We have that option also: