Most gift card transactions take less than 10 minutes. However, trades are attended to in a first-in-first-out order.
Also, there are some gift cards that take a longer time to process. Here is a list of them:
Walmart
Apple Store
eBay (Most times)
Vanilla
VISA
Walmart VISA
Best Buy
Nordstrom
American Express
NIKE
Target
Sephora
Footlocker
JCPenney
Macy's
Mac
Saks Fifth Avenue