If you paid for the item with your outstanding PayPal balance, the refund should show up very quickly, as in a matter of hours.
If you paid for the item via PayPal but used an attached credit or debit card, the refund will probably take 3-5 business days, since the CC needs to be notified of the refund.
If you paid for the item via PayPal but used an attached checking account, the refund will probably take 3-10 business days, this you basically "paid by check", and checking account systems are just plain slow for processing refunds.