.open > .dropdown-menu {
 opacity:1; visibility:visible; 
}
.dropdown:hover .dropdown-menu, .btn-group:hover .dropdown-menu { opacity:1; visibility:visible; }

.dropdown-menu {
  opacity:0;
  display:block;
  visibility:hidden;
  
  transition: all 0.2s ease-out 0.5s;
  -webkit-transition: all 0.2s ease-out 0.5s;
}
.navbar-default .navbar-nav > li.dropdown:after{
  opacity:0;
  visibility:hidden;
  display:block;
  
  transition: all 0.2s ease-out 0.5s;
  -webkit-transition: all 0.2s ease-out 0.5s;
}
.dropup .dropdown-menu {
  -webkit-transform-origin: bottom;
  transform-origin: bottom;  
}

.navbar .nav > li > .dropdown-menu:after {

}