JSFiddle - React, Tailwind, and code Playground

HTML

<ul>aaa
    <li>ффф</li>
</ul>

CSS

li {
    display:none;
}

JavaScript

var timer;
$('ul').hover(function () {
    clearTimeout(timer);
    timer = setTimeout(function () {
        $('li').slideDown()
    }, 1000);
}, function () {
    clearTimeout(timer);
    $('li').slideUp();
});