I think its always taken a while (1-2 weeks) but I was told in December that it would take a bit longer because of the holidays. Plat phone agent verified that it was "in process." Sure enough had the refund 2-3 weeks after cancellation.

I believe the refund department looks at all cancellations manually to verify that they are entitled to a refund and therefore it takes a bit of time. It seems like they could enter a simple command into their software to refund automatically if you cancel within 24 hours.