Have you had an email from Ebay (not the seller) confirming that your cancellation was accepted and that the seller is processing a refund?
If so, then your refund is 'in the system' but how long it takes for you to get it back will vary and nobody can tell you accurately how long it will take for the refund to arrive with you. Refunds do seem to be processed by Ebay very quickly; the delay in you receiving the payment is variable.
I have found Paypal refunds are really fast - arriving very soon after the email from Ebay - minutes, rather than hours.
As you realise, refunds to your bank can take several days (they may show up in 'pending' sooner) and refunds to credit cards can take up to 30 days.
So, based on my own experience:
Ebay process refunds really quickly but it can take a while for you to get the money back.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)