Explain to your buyer that the 3 - 5 day notification is a tad to say the least, misleading.
Refunds go back to original payment source, and it's not instant.
If they paid with PayPal it goes back to a PayPal account fairly swiftly.
Paying with a debit / bank card? Can take up to 12 days to appear back in your bank account.
Credit card payment? This takes the longest, up to 30 days to appear back in the card account used.
@lordof-1127