Let's see at a high level how Aura works. Aura requires the same list of validators to be specified in each node. This is a list of account addresses that participate in the consensus. A node may or may not be a validating node. Even a validating node needs to have this list so that it can itself reach a consensus.
This list can either be provided as a static list in the genesis file if the list of validators is going to remain the same forever, or be provided in a smart contract so that it can be dynamically updated and every node knows about it. In a smart contract, you can configure various strategies regarding who can add new validators.
The block time is configurable in the genesis file. It's up to you to ...
