It depends on which reward you want to redeem your diamonds for. You can check all the rewards here and more rewards will be added soon as well.
https://coinmarketcap.com/account/rewards/
You can even redeem diamonds now , I saw there are lot of rewards that you can purchase with 100-500 diamonds , like avatar rewards. But I suggest not to purchase that kind of rewards. If we keep collecting daily , we can purchase a good NFT probably for 10000 diamonds which is more worth than those cheap avatar rewards.
It's not in beta stage. There are already 2 or so NFT rewards but their price is high , around 21k diamonds and another one 3k diamonds , which will take time for us to earn and purchase that nft. More nft rewards will be added soon though.
Here are some pics of those nft rewards.