Miriam de Paula

WP Coming Soon is a plugin that adds a countdown clock in the Coming Soon page. This plugin uses Keith Wood jQuery plugin. See it at: http://keith-wood.name/countdown.html.
[BASIC USAGE]
Put this <code>if ( function_exists('get_countdown')) get_countdown();</code> where you want to display the countdown clock…
If you want to use the countdown timer within a page or page template, you can use the shortcode <code>[wp_coming_soon]</code>

WP Coming Soon

WP Coming Soon is a simple plugin that adds a countdown clock in your Coming Soon page... Nothing more!

Deligence Technologies

A Plugin with easy customization to display date and time of multiple timezones. All settings are available from Admin panel.You can show up to 4 different clocks using this plugin. 
You can also use as a shortcode in posts and pages. It’s shortcode format is [DT_World_Clock title:timeZone:locale,title:timeZone:locale,timeZone].
Let suppose if you want to display a world clock within a page and post then you have to use the shortcode. In [DT_World_Clock title:timeZone:locale,title:timeZone:locale,timeZone:locale], DT_World_Clock is the name of shortcode and ‘title:timeZone:locale,title:timeZone:locale,timeZone’ is the parameter of shortcode. Here title is the title of clock and timeZone is used to show the date and time of this timeZone. if you want to show title of clock then you have to provide the title otherwise it is not required.
In order to use shortcode, you have to edit the post and page and put the shortcode in content of this post and page.
For example
if you want to show one clock then use [DT_World_Clock clock1:Indian/Cocos:en_GB]
if you want to show two clocks then use [DT_World_Clock clock1:America/Creston,clock2:Europe/Moscow]
if you want to show two clocks but you do not need the title of first clock then use [DT_World_Clock America/Creston,clock2:Europe/Moscow]
if you want to show three clocks then use [DT_World_Clock clock1:America/Creston,clock2:Europe/Moscow,clock3:America/Aruba]
If you want to display more clocks – you can go for our pro version. You’ll be able to add up to 200 clocks. At the cost of $14 – you’ll get this plugin (source code) which you’ll be able to add at any number of websites and will also get support for one domain for 6 months. Here is the link to purchase the pro version – 
<a href="https://1.envato.market/c/1305001/275988/4415?u=https%3A%2F%2Fcodecanyon.net%2Fitem%2Fwordpress-world-clock-multiple%2F14960349" rel="nofollow ugc">https://1.envato.market/c/1305001/275988/4415?u=https%3A%2F%2Fcodecanyon.net%2Fitem%2Fwordpress-world-clock-multiple%2F14960349</a>

DT World Clock

A Plugin that can be easily set to display date and time of multiple timezones. Supports date and time formatting

WP Coming Soon vs DT World Clock