I saw mine on my credit card statement in 2 business days, which was pretty impressive, but normally I'd say 3-5 business days is the average if you're banking with a major US bank (longer with a smaller local bank/card issuer).
As others have said, it depends on your bank/cc company. Disney tells you it could take up to 2 billing cycles, but I've never had it take that long as I've had refunds show up within 2-3 days of cancelling (my bank might just process quickly). With that said, I've had Disney gift cards credited by the next day.
It has taken about a week to ten days in my experience although it may depend on the credit card. We usually use Chase or Amex and both have been fairly quick.
I actually canceled a paid in full reservation made through a third party last week, which meant there was an extra level of processing to go through for the cancellation, and I got an email about the credit from Amex in three days. I really didn’t expect it to come through so quickly. I moved my trip up from September to August and was trying to time it so the credit would hit the same billing cycle as the charge for the rescheduled trip. I have had pretty good luck with Amex refunds hitting promptly.