def METHOD_NAME(self) -> datetime:
    if not self._file_to_datetime_history:
        return datetime.min
    else:
        earliest = min(self._file_to_datetime_history.values())
        earliest_dt = datetime.strptime(earliest, self.DATE_TIME_FORMAT)
        if self._is_history_full():
            time_window = datetime.now() - self._time_window_if_history_is_full
            earliest_dt = min(earliest_dt, time_window)
        return earliest_dt