How long does it take to refund credit back on credit card?

I recently made an online purchase and on my card account and saw it was charged twice. I contacted the merchant on Monday and they responded and gave credit back on the card but I checked the account balance and the account remains unchanged. Now it is Wednesday and I still do not see the balance changed. Is the merchant taking their time to process or the credit card company? If it matters the card i used was capital one mastercard.