Packard smiles in agreement. "At midnight. If you stay here—" he checks his watch "—for another four hours, you will see fresh intercepts coming in from the Y Service that will produce utter gibberish when we run them through the Typex, because the Jerries will have changed all their codes on the stroke of midnight. Rather like Cinderella’s magic carriage turning back into a pumpkin. We must then analyze the new intercepts using the bombes, and figure out the day’s new codes."