If you add the code {complete_date} in the email template, the date of purchase is not inserted. Use this code to show the purchase date. The only issue I can see with this is, if the card is sent in a date in the future then the amount of available time to use it will be reduced. So for example, I buy a card today for a birthday and the the birthday is not until next month and I set it to be sent out in 28 days time, then the receiver would lose 28 days to redeem the Gift Card. It should be from the date the electronic card is received.
To add the purchase date of the Gift Card:
That info is not available in gift card email. If you want to add it by yourself, you edit
administrator/components/com_cmgiftcard/helpers/cmgiftcard.php
search for the line
'{gift_card_message}' => $card->message,
and add this line after it
'{completed_date}' => JHtml::_('date', $card->completed, 'DATE_FORMAT_LC2'),