Well, you can't do that in PHP. Since PHP is server-side and waiting (you said 3-5 seconds) is client-side, you'll have to use client-side coding. This can be achieved via JavaScript or meta tags. I recommend the latter, as it is more accepted of a method, and more browsers recognize it.
The HTML tag would look like this:
<meta http-equiv="refresh" content="3;URL=newpage.php">
Notice the 3 in there. That's the second count before they are redirected.