const onTimeout = el => el.style.display = 'block';
document.querySelectorAll('.x').forEach((n, i) => {
setTimeout(onTimeout, i * 1000, n);
});
или
let index = -1;
const intervalId = setInterval(items => {
const el = items[++index];
if (el) {
el.style.display = 'block';
} else {
clearInterval(intervalId);
}
}, 1000, document.querySelectorAll('.x'));
или
(function next(items, index) {
if (items[index]) {
setTimeout(() => {
items[index].style.display = 'block';
next(items, index + 1);
}, 1000);
}
})(document.querySelectorAll('.x'), 0);