Who generates the timestamp on a transaction?

When a transaction is given a consensus timestamp, the network of nodes, as a whole, generates that timestamp. The hashgraph shows the time at which each node first received the transaction. The consensus timestamp is defined to be the median of those different times from a subset of the full network. Virtual voting is the Byzantine agreement mechanism that determines which nodes contribute a time to the median calculation. If more than 2/3 of participating nodes are honest and have reliable clocks on their computers, then the timestamp itself will be honest and reliable, because it is generated by an honest and reliable node, or falls between two times that were generated by honest and reliable nodes. In Hedera's proxy staking system, a transaction is entered into consensus after nodes with a stake of more than 2/3 of hbars validate a transaction (i.e., not after more than 2/3 of the number of nodes validate it).