Need to "gift" an app purchased in google play by issuing a refund later. How many days can I wait to refund?
The refund button on the Play store is only available for 2 hours (although Google's support pages say 15 minutes).

From your question it sounds like you may be the developer of the app, in which case you can manually refund the purchase regardless of when the app was purchased via your Google Wallet merchant account. I don't think this actually reverses the purchase (they can still install and use the app) but the cost of the purchase is refunded to the user.