mon.js

setFakeTime();

const startTimeMon = performance.now(); // set startTime with monotonic clock

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

const endTimeMon = performance.now(); // set endTime with monotonic clock
const durationMon = endTimeMon - startTimeMon;

console.log(`Duration measured by monotonic clock\t: ${durationMon}ms`);