You have to set Notify user that automatically redirect to different site after timeout.
In Visual Policy Manager create new Web Access Layer...
1. Right click on Action>Set>>New...>Notify User>
2. Notify mode - check "Notify on every host"
3. Body:
<script type="text/javascript">
setTimeout(function(){window.location.replace('https://test.site')},5000);
</script>
<body onload="Accept();var notify_img=new Image(1,1);notify_img.src='$(exception.details)';">
<p align=center><text align=center><b><span style='color:red'><h2>Important Notice!</h2></span></b></p>
<p><b>System maintenance is scheduled for Sunday July 17, 2:00-4:00 am EST.</b></p>
<p><b>To report any conflicts with the scheduled maintenance, see $(exception.contact)</b></p>
<p><b>PLEASE NOTE:</b> Internet usage is routinely monitored and logged.</p>
<p>Your IP address: $(client.address)<br>
Your username: $(user)</p>
<p>You will be connected in 5 seconds.</p>
</body>
This script will redirect you to "test.site" after 5 seconds.