Attach the following script to an object, it sends some timestamps between two clients, measuring the one-way trip times. Observe the results in the debug log with 2 local clients on a live server

(or assign a TMPro.TextMeshProUGUI field in the inspector for easier viewing)

Comparing packet age times on the local clock compared to server derived times shows discrepancy, this varies even within the same instance upon rejoining (though this cannot be easily tested with the script included, you'd need to remake the instance or rejoin on both clients)

Shouldn't measuring player2_receiveUTC - player1_sendUTC be equal to player2_receiveServerTime - player1_sendServerTime if both player1 and player2 are run on the same machine?