primer

//bg.php datoteka
<?php
echo time();
?>

//index.html datoteka
<h1 id="cas"></h1>
<script>
var xhttp = new XMLHttpRequest();
xhttp.onload = function() {
	cas.innerHTML = this.response;
};

setInterval(function(){
  xhttp.open("GET", "bg.php", false);
  xhttp.send();
},1000);
</script>