Navigate to a webpage and then redirect after X seconds

Navigate to a webpage and then redirect after X seconds

I am not a php programmer so bear with me on this one... I am trying to
navigate to a specific URL and then redirect to another page after 3
seconds. However, the second line of the redirect does not work!
Please see below my php code
<?php
header("Location: http://someurl.com");
header("Refresh: 3;url=http://www.somenewurl.com/index.php");
?>
I reached the first URL - meaning the first line is executed. However, the
redirect in the second line does not happen...