The reward probabilities can be found here.

You can view it by clicking Reward Wheel Probabilities under "How It Works".

You will immediately start Platinum Whale as you as you have completed Gold Whale 1. Due to current system limitations, you will not be able to see your Fish Buffet Spin Wheel when this occurs BUT you will receive the prize nonetheless as the spin will run in the background.
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History and results of that spin will be available in your Fish Buffet history on the application or you can check your recent cashier transaction history by selecting rewards.