Staking rewards are allocated each era, but there is a manually step that needs to occur in order to receive the rewards, the reward payouts need to be initiated for each validator in each era. As soon as a validator or staker requests a payout for an era, all the stakers for that validator will receive the rewards into their accounts. Each user does not need to claim individually and it is recommended that validators claim rewards on behalf of their stakers as soon as an era ends. Reward payouts for can be initiated by any account.