code: public TimeDuration durationFrom(Timestamp reference) {
          long nanoSecDiff = nanoSec - reference.nanoSec;
          nanoSecDiff += (unixSec - reference.unixSec) * 1000000000;
          return TimeDuration.ofNanos(nanoSecDiff);
      }
docs: Calculates the time passed from the reference to this timeStamp.
  The result is the relative time from the reference to this
  timestamp, so that reference + result = this.
  
  @param reference another time stamp
  @return the duration from the reference to this