Wrong way to measure execution time in Node.js

WrongWayToMeasureExecutionTime.js

var sleepFunction = function(milliSecondsToSleep) {
    let startTime = new Date().getTime();
    setTimeout(function() {
        console.log("Dummy CallBack");
    }, milliSecondsToSleep);
    let endTime = new Date().getTime();
    console.log("My job done in " + (endTime - startTime) + " ms");
}

let startTime = new Date().getTime();
sleepFunction(1000);
sleepFunction(1000);
let endTime = new Date().getTime();
console.log("Program took " + (endTime - startTime) + " ms to complete");