Rather than handling each block separately, proof-of-stake chains group them into epochs. Validator duties are assigned per epoch, rewards are tallied per epoch, and finality is usually declared at epoch boundaries.
Epochs matter operationally. Entering or exiting the validator set, and therefore unstaking, happens in epoch-sized steps with queues, which is part of why an unbonding-period exists.
Example: 32 slots of 12 seconds is a 6.4-minute epoch, and finality after two epochs is about 12.8 minutes. If you are planning to unstake into a falling market, add the exit queue on top of that; it can run from hours to weeks when many people leave at once.
Related: proof-of-stake, validator, finality, unbonding-period