document.addEventListener('DOMContentLoaded', function() {

        var div1 = document.getElementById('div1');

        var div2 = document.getElementById('div2');

​

        div1.addEventListener('mouseover', function() {

            setTimeout(function() {

                div2.style.display = 'block';

            }, 500);

        });

​

        div1.addEventListener('mouseleave', function() {

            setTimeout(function() {

                div2.style.display = 'none';

            }, 500);

        });

    });