I recently ordered two cards, one of which came through immediately. I had to call about the other one - they told me it was “stuck in the send queue” and it took them a couple of days to rectify it. Thus best not to purchase too close to final payment date in case of a delay.
Also, one thing to consider is that if you should cancel any of your bookings or purchases made with the gift card, the funds are returned to the gift card, not to your credit card. So you are essentially left with a “future cruise credit” rather than an actual refund.