Redirecting to index.html

Hello,
I am lost – sometimes this solution works, sometimes not:
I am sometimes developing a WP site in the background of a HTML site.
Using this plugin, I am able to have visitors see the HTML site, whereas the logged in user sees the WP homepage.
To get there, I usually ener a
<script>// <![CDATA[
var url =’http://blabla.com/index.htm&#8217;; var delay = 0; var d = delay * 1000;window.setTimeout (‘parent.location.replace(url)’, d);
// ]]></script>
into the Custom HTML area.

Question: It doesn’t work all the time. What is the correct way to do this?

Thanks!

https://wordpress.org/plugins/ultimate-coming-soon-page/