ho provato questo e sembra funzionare:
codice:
<!DOCTYPE html>
<html>
    <head>
        <title>TEST</title>
        <meta charset="UTF-8">
        <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
        <script>
            $(document).ready(function () {
                $('#preloader').fadeOut(5000);
            });
        </script>
    </head>
    <body>
        <div id="preloader" style="border: 1px solid black;"></div>
    </body>
</html>