A blockchain doesn't, unless all peers are directly connected to all other peers. Otherwise, a transaction has to propagate through the network. For Bitcoin,

A blockchain doesn't, unless all peers are directly connected to all other peers. Otherwise, a transaction has to propagate through the network. For Bitcoin, for the last couple years, looks like it's typically 15ish seconds to reach 90% of the network and 5ish to reach 50% of the network. A centralized server could send updates to directly connected clients much faster than that. https://www.dsn.kastel.kit.edu/bitcoin/#propdelaytx https://www.dsn.kastel.kit.edu/bitcoin/#propdelaytx