<ul class="nav">
    <li><a href="#">item1</a></li>
    <li><a href="#">item2</a></li>
    <li><a href="#">item3</a></li>
    <li><a href="#">item4</a></li>
</ul>

.nav {cursor:default;}
.nav li {
    display:inline-block;
    border:1px solid black;
    margin:0 10px;
    background:#eee;
}
.nav li a {
    display:inline-block;
    text-decoration:none;
    color:blue;
    padding: 4px 8px;
}
.nav li + li {
    opacity:0;     
    
    -webkit-transition-property:opacity;       
    -moz-transition-property:opacity;  
    -o-transition-property:opacity;  
    transition-property:opacity;       
    
    -webkit-transition-timing-function: ease-in;     
    -moz-transition-timing-function: ease-in;
    -o-transition-timing-function: ease-in;
    transition-timing-function: ease-in;  
}
.nav:hover li + li {
    opacity:1;

    -webkit-transition-duration: 0.5s;
    -moz-transition-duration: 0.5s;
    -o-transition-duration: 0.5s;
    transition-duration: 0.5s; 
}
.nav:hover li + li + li {
    -webkit-transition-duration: 1s;
    -moz-transition-duration: 1s; 
    -o-transition-duration: 1s;
    transition-duration: 1s; 
}
.nav:hover li + li + li + li {
    -webkit-transition-duration: 1.5s;
    -moz-transition-duration: 1.5s;
    -o-transition-duration: 1.5s;
    transition-duration: 1.5s; 
}​