timesnippet.js

setFakeTime();

const startTimeToD = Date.now(); // set startTime with time-of-day clock
const startTimeMon = performance.now(); // set startTime with monotonic clock

setImmediate(() => {
  correctTimeNTP(); // synchronise the clock
});
await doSomething();

const endTimeToD = Date.now(); // set endTime with time-of-day clock
const endTimeMon = performance.now(); // set endTime with monotonic clock
const durationToD = endTimeToD - startTimeToD;
const durationMon = endTimeMon - startTimeMon;
const error = (durationToD - durationMon) / 1000;

console.log(`Duration measured by time-of-day clock\t: ${durationToD}ms`);
console.log(`Duration measured by monotonic clock\t: ${durationMon}ms`);
console.log(`Error: ${error.toFixed(3)}s`);