Sending an e-mail confirmation of a refund is an extra step they have to take when processing it. My experience is they don't send one unless you ask for it. They often seem surprised when I ask them to do so.

But I wouldn't worry about it, the refund has likely been processed. Refunds don't show up in pending state on credit cards the same way charges do, so 24 hours is not long enough to wait during the week, let alone on a weekend. I'd give it a week before even thinking about contacting WS.