Timeout does not guarantee time to executoin

firstLesson.js

// Select all, copy-paste it in the console and try it out.
const expectedMilliseconds = 1000;
const startTime = new Date();

const logOne = () => console.log(1);
const logTwo = () => {
  // This should be close to 0
  console.log("Diff:", (new Date() - startTime) - expectedMilliseconds);
  console.log(2);
}
const logThree = () => console.log(3);

logOne();
setTimeout(logTwo, expectedMilliseconds);
logThree();
// Below this line you should see the console.logs
// -----------------------------------------------

longer.js

// Select all, copy-paste it in the console and try it out.
const expectedMilliseconds = 1000;
const startTime = new Date();

const logOne = () => console.log(1);
const logTwo = () => {
  // This should be close to 0/
  console.log("Diff:", (new Date() - startTime) - expectedMilliseconds);
  // But is actually much more than 1 second.
  console.log(2);
}
const logThree = () => console.log(3);

logOne();
setTimeout(logTwo, expectedMilliseconds);
logThree();

// Let's keep the Stack busy
for (let i = BigInt(0); i < BigInt("40000000"); i++) {
  // Some long calculation
  let a = i * i + i / BigInt(4);
};
// Below this line you should see the console.logs
// -----------------------------------------------