Gemini will send you any earned rewards after it receives them from the relevant network. Different networks have different reward distributions. For example, in the case of Eth2, users can withdraw their Eth2 rewards only after Eth2 and the ethereum network merges with the mainnet. In the case of MATIC staking, users will receive their rewards within one block confirmation after requesting redemption.
Staked ETH may also take up to 15 days to get activated on the Beacon Chain, so you should expect a delay between when you choose to stake your ETH and when rewards begin accruing in your account.