Here is the code to introduce custom navigation hover/unhover delay. This is a javascript file and I added this to master page.

var constShowDelay = 350;
    var constDisappearDelay = 100;
    var myVar;
    var myTimeoutID;
    var myNode, myData;
    var ref_Menu_HoverStatic;
    var ref_Menu_Unhover;
    var ref_overrideMenu_HoverStatic;

function Func_Menu_HoverStatic(item) {

       Func_overrideMenu_HoverStatic(item);
    }

    function Func_overrideMenu_HoverStatic(item) {
        var node = Menu_HoverRoot(item);
        var data = Menu_GetData(item);
        myNode = node;
        myData = data;
        if (!data) return;
        myVar = item;
        myTimeoutID = setTimeout("Func_DelayExpandMenu(myNode,myData)",
        constShowDelay); 

    }

    function Func_DelayExpandMenu(node, data) {
        __disappearAfter = constDisappearDelay;
        Menu_Expand(node, data.horizontalOffset, data.verticalOffset);
    }

    function Func_Menu_Unhover(item) {
        clearTimeout(myTimeoutID);
        ref_Menu_Unhover(item);
    }

function _NavigationDelay(){

if ((typeof (Menu_HoverStatic) != 'undefined')) {
            ref_Menu_HoverStatic = Menu_HoverStatic;
            Menu_HoverStatic = Func_Menu_HoverStatic;
            ref_Menu_Unhover = Menu_Unhover;
            Menu_Unhover = Func_Menu_Unhover;
            ref_overrideMenu_HoverStatic = Menu_HoverStatic;
            Menu_HoverStatic = Func_overrideMenu_HoverStatic;
        }

}