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.

saill

Lets you set a date to launch or suspend your site automatically. Lets you choose which admins have access to the plugin settings. Generates beautiful Coming Soon and Site Suspended pages with customizable background image or color and and an optional message box that can also allow users to log in from the coming soon page. Alternatively allows you to redirect to a different URL. This plugin is based on the <a href="https://wordpress.org/plugins/underconstruction/" rel="ugc">underConstruction</a> plugin. A complete description along with screenshots and usage instructions is <a href="http://www.wickedcleverlabs.com/site-launcher/" rel="nofollow ugc">here</a>.

Site Launcher

Timed launch or suspension of your site with custom "site unavailable" pages or with a redirect.

SM CountDown Widget vs Site Launcher