(function () {
	let counter = 0;

	const countdown = () => {
		let inner_timeout = setTimeout(countdown, 1000);
		if (counter === 5) {
			clearTimeout(inner_timeout);
		}
		console.log(counter === 5 ? console.log("поехали!") : 5 - counter);
		counter++
	}

	setTimeout(countdown, 1000);
})();

// или

for (let i = 0; i <= 5; ++i) {
	setTimeout(() => {
		i === 5 ? console.log("поехали!") : console.log(5 - i);
	}, 1000 * i);
}