Gambling Policy on In-App Redeemable Gift Cards

Can anyone give any advice on Apple's policy regarding Amazon gift cards/gift codes, which can be redeemed in-app, based on a virtual currency generated by the User's time spent active on the App.

To summarize, user X and user Y play a game and spend 2 hours of time playing. For 2 hours, they generate 10 Diamonds which can be then redeemed for a $10 gift card on Amazon. The user will receive a gift code/card to the email registered to him/her in the game.

My understanding is this does not violate section 5.3 of Apple's gambling definition as it is time-based.