By that time' is a common phrase used in speech and writing to indicate a certain point in time. It can be replaced with synonyms such as "by then," "by the hour," "at that time," "at that point," "by that moment," "by the specified time," and "by that particular time." These words convey a similar meaning and indicate a specific time when an event took place or will take place. "By that time" is a versatile phrase that keeps the reader or listener up to date with the conversation or story being told. It also helps in creating a smooth flow of transition and understanding between different events or actions.