sierramike

This widget allows you to display a JQuery responsive countdown timer on your website. You can use it as a widget or include it wherever shortcodes are supported.
It comes out of the box with french and german translations.
The widget contains media queries in its css stylesheet. You can edit it to suit your needs.
This widget also supports shortcodes!
Just add a [smcountdown timerdate=’xxx’] shortcode to any of you posts and you’ll get a responsive countdown timer! 
The shortcode supports one parameter: timerdate. 
* timerdate indicates the target date until which the timer counts down
Shortcode usage samples : 
[smcountdown timerdate=’2015/12/31 23:59:59′] 
Displays a countdown timer until Decembre 31th of 2015, 23h59m59s.

SM CountDown Widget

Displays a responsive JQuery countdown timer.

Florent Maillefaud

The WP Maintenance plugin allows you to put your website on the waiting time for you to do maintenance or launch your website. Personalize this page, pictures and countdown with:
<h3>Features</h3>
<ul>
<li>Choice texts colors and fonts</li>
<li>Upload logo picture</li>
<li>Upload background picture or pattern</li>
<li>Countdown</li>
<li>Custom Code Header for Analytics ready</li>
<li>Social Networks ready</li>
<li>Customize CSS</li>
<li>Insert for shorcode (Newletter or Contact form)</li>
<li>Enable “503 Service temporarily unavailable”</li>
<li>Choose access by Roles and Capabilities</li>
<li>Choose access by ID Pages</li>
<li>Choose access by IP addresses</li>
</ul>
wp-maintenance.pot file available

WP Maintenance

Create and customize your maintenance page

SM CountDown Widget vs WP Maintenance