I am speaking from my own experience. I have my debit card (and a credit card) linked to my paypal account. I also have experienced a lot of time passing between initiating a refund and the person receiving the same, to the extent that I have offered after that - that I can pay to the person's email address, which does seem to be instant. Since I have had this happen to me I wanted to offer my twopenneth that a refund is not necessarily instant. I am sorry if the link I happened to find was American rather than English.
Here is the UK Ebay view on this
http://pages.ebay.co..../buy/return-item.html
Receiving the refund
You will be notified via email as soon as the seller indicates that they will initiate the refund. Usually they will send the refund within a couple of days, and at the latest 30 days, after you’ve started the return.
After the seller has sent the refund to your PayPal account, the case will close automatically. You can transfer the money from your PayPal to your bank account or use the PayPal balance for other purchases on eBay.
Timeframes: A business seller is legally obliged to issue the refund within 30 days after they accepted your return or the cancellation of your contract with them.
Even if a business seller issues the refund immediately, it may take several days before the money is transferred to your account.
The last sentence says it all.