I have an HTML splash screen that I wanted to disappear automatically after 5 seconds. In case this helps anyone else, my solution is to add a meta refresh. I am not sure how you might do this if you are displaying another Drupal page as your splash page.

<html>
<head>
<meta http-equiv="refresh" content="5; url=http://mydomain.com/?splash=off">
</head>
<body>
<center>
<a href="/">Click to Enter<br>
<img src="/sites/mydomain.com/themes/mytheme/images/splash_image.jpg">
</a>
</body>
</html>