code: public static TimingInfo unmodifiableTimingInfo(long startEpochTimeMilli, long startTimeNano, Long endTimeNano) {
          return new TimingInfoUnmodifiable(startEpochTimeMilli, startTimeNano, endTimeNano);
      }
docs: Returns an instance of {@link TimingInfo} that is not modifiable.
  
  @param startEpochTimeMilli start time since epoch in millisecond
  @param startTimeNano start time in nanosecond
  @param endTimeNano end time in nanosecond; or null if not known