function startbanner() {
   var x = document.getElementById("werbung");
   setTimeout('document.getElementById("werbung").style.visibility = "visible";',500);
   setTimeout('document.getElementById("werbung").style.visibility = "hidden";',12000);
}

function endebanner() {
   var x = document.getElementById("werbung");
   x.style.visibility = "hidden";
}