Need to "gift" an app purchased in google play by issuing a refund later. How many days can I wait to refund?

I know Google play still doesn't support gifting of apps but I need to provide one of my clients a free copy. They already purchased it. I am going to refund them later, after they are done using the app. **How many days from purchase are valid for issuing a refund?** I can't find this answer online. I see some other purchases made >30 days ago that are refundable, but I don't know if I can wait 60 days? 90 days? 120? Can someone login to their Google Wallet and see how far back the refund button is available?