A new set of validators is selected for each era, which is a duration of 12 hours, and the set of validators is selected 2 eras before. For example, validators running in era 10 were elected in era 8. Parameters set for each validator including the stake amount, the validator's commission rate, etc, are fixed as well during the selection. For example, if a validator changes the commission from 10% to 20% in era 10, the 20% commission won't take effect until era 12. This is also true for stakers when they select validators. If a staker nominates validators A, B, and C in era 10, the nominator's funds will be locked for staking in era 10, but they will count toward validators A, B, and C in era 12. While staking, the staked tokens are locked (bonded) and there is a 7 day period before staked funds can be transferred.