1. If from their balance it would be instant BUT then it would depend on your funding source as to how long your bank or card issuer takes to process the refund back to your bank account or card.
2. If from their bank account then it would go as an echeque and take 5-7 days to clear through to paypal who will again then pass it on to your funding source and again how long is dependent on the time your bank or card take to process the refund.
Advice is voluntary. Kudos / Solution appreciated.