why my vad show quickly even m settting time on that to display

here is my code



<div id="vad">
<div id="adcode">

CODE SHOW HERE
</div>
<div id="cbut" onClick="document.getElementById('vad').style.display='none'">CLOSE</div>

</div>

<script>

k=setInterval('document.getElementById("vad").style.visibility="visible"',20000);

v=setInterval('document.getElementById("cbut").style.visibility="visible"',30000)

</script></div>