allora apre come popup

<script>
function apri() {
var a = window.open("pippo.html","nomefinestra","width=500 ,height=400");
}
</script>

<body onLoad="apri()">

a tempo

<script>
function apri() {
var a = window.open("pippo.html","nomefinestra","width=500 ,height=400");
}
</script>

<body onLoad="setTimeOut('apri()', 10000)">