example.js

function timeFormatter (milliseconds) {
  const padZero = (time) => `0${time}`.slice(-2);

  const minutes = padZero(milliseconds / 60000 | 0);
  const seconds = padZero((milliseconds / 1000 | 0) % 60);
  const centiseconds = padZero((Math.round(milliseconds / 10) | 0) % 100);

  return `${minutes} : ${seconds} . ${centiseconds}`;
}

// Example stopwatch times
const timeIntervals = [
  {
    startTime: 1472104779284,
    stopTime: 1472104782441
  },
  {
    startTime: 1472104782442,
    stopTime: 1472104785081
  },
  {
    startTime: 1472104785081,
    stopTime: 1472104788368
  },
  {
    startTime: 1472104788369,
    stopTime: 1472104791475
  }
];

// Calculate time it took for each entry
const times = timeIntervals.map(time => time.stopTime - time.startTime);

// Run the timeFormatter on each individual time
const individualTimes = times.map(timeFormatter);

// Run the timeFormatter on the sum of all the times
const mainTimer = timeFormatter(times.reduce((a, b) => a + b));

/**
 * [
 *   '00 : 03 . 16',
 *   '00 : 02 . 64',
 *   '00 : 03 . 29',
 *   '00 : 03 . 11'
 * ]
 *
 * (Adds up to 00 : 12 . 20)
 */
console.log(individualTimes);

/**
 * 00 : 12 . 19
 */
console.log(mainTimer);