Sergio Carracedo 
On more than one occasion, it has happened to us that once work on a website is finished, the client requests that it not be published instantly, but rather that a page appears showing a countdown and that once this count reaches 0, the site goes online.
Traditionally, we did this manually, but it has several disadvantages, such as having to be alert to publish the site. Therefore, we decided to create a Drupal 7 module that would allow this task to be done automatically and that would also be easy for the client to manage in case they needed to adjust the countdown deadline.
We call this module Site publish countdown and it is currently in the Drupal module sandbox: https://www.drupal.org/sandbox/sergiocarracedo/2718591
This module, once installed and activated, allows the website administrator to set the launch date before which it will redirect all anonymous visits (to any URL) to the countdown page.
The site administrator or administrators will be able to log in as usual, and they will be able to see the website normally to perform tasks before the site launch.
Once the countdown is over, the page itself will reload, showing the normal version of the site.
This module allows developers to layout and customize the countdown page; it is only necessary to add the file sitepublishcountdown.tpl.php in the folder of the theme used by the web (and clear the theme registry). The only mandatory content of this file is the following line:
<time datetime="<?php print $datetime; ?>"><?php print $datetime; ?></time>which is responsible for displaying the countdown. The rest is at the site designer’s disposal so they can customize it.