Refund

Apple say:

Once you’ve submitted your cancellation request, the status message of that item will read Canceled or Pickup Canceled. If you canceled an item that was shipping to a physical address, you will not be billed for your item. If you canceled a pickup item, you may have been billed. We will initiate your refund immediately after you submit your cancellation request.

https://www.apple.com/shop/help/viewing_changing_orders

If you are due for a refund it can take up to 30 days if you used a credit card (this happens with any card purchases, its not just Apple).

According to Apple's page on refunds from App Store/iTunes etc this can also be up to 30 days. That doesn't necessarily mean it will take that long: but it's up to your bank.