code: function getHrTimeDurationInMs (startTime, endTime) {
      if (startTime === null || endTime === null) {
          return null;
      }
  
      var secondDiff = endTime[0] - startTime[0];
      var nanoSecondDiff = endTime[1] - startTime[1];
      var diffInNanoSecond = secondDiff * NS_PER_SEC + nanoSecondDiff;
  
      return Math.round(diffInNanoSecond / MS_PER_NS);
  }
docs: Get duration in milliseconds from two process.hrtime()
  @function getHrTimeDurationInMs
  @param {Array} startTime - [seconds, nanoseconds]
  @param {Array} endTime - [seconds, nanoseconds]
  @returns {Number|null} durationInMs