Antonio D.

Daniil Zhitnitskii

This plugin provides network administrators ability to set same time zone over all blogs in multisite installation in one click, and also it restricts changes of timezone from local blogs settings.
*Based on: https://premium.wpmudev.org/forums/topic/set-default-timezone-for-new-blogs-in-the-network
Only works with multisite installation!
Gutenberg: compatible!
<h3>Disclaimers</h3>
The Simple default timezone plugin is supplied “as is” and all use is at your own risk.

Simple default timezone

As Super Administrator, you can set the (default) timezone for all blogs.

JB Christy

This WordPress plugin adds the <code>[localize_time]</code> shortcode. The shortcode allows an author 
to enter a date and time in any timezone. The shortcode displays the original time with 
timezone, followed by the same time in the user’s timezone, formatted correctly for the 
user’s locale. This is useful for announcing live events, e.g. a live online streaming 
event, to widely dispersed audiences.
The date and time to be displayed are entered as the shortcode’s content, i.e. between the 
<code>[localize_time]</code> and <code>[/localize_time]</code> tags. The time can be specified in almost 
any format that’s recognizable as a date and time.
The shortcode takes the following options:
<ul>
<li><code>tz</code> – the timezone the shortcode’s content is in. If this option is omitted, it defaults 
to the site’s timezone. Timezones are specified in any format recognized by 
<a href="http://www.php.net/manual/en/timezones.php" rel="nofollow ugc">PHP’s DateTimeZone</a>.</li>
<li><code>fmt</code> – a format string specifying how the original time should be displayed. If omitted, 
it defaults to the site’s date format followed by the site’s time format followed by the 
timezone. To output the original time exactly as entered (with the timezone), specify 
<code>fmt="orig"</code>. Or you can enter a format string using the same codes that are used on 
WordPress’s General Settings tab. See 
<a href="https://codex.wordpress.org/Formatting_Date_and_Time" rel="nofollow ugc">full documentation on date / time format strings here</a>.</li>
<li><code>before_local</code> – the string to precede the local time. Defaults to ‘ (‘</li>
<li><code>after_local</code> – the string to follow the local time. Defaults to ‘)’</li>
</ul>
<h3>Examples</h3>
Below are examples of using the shortcode. For these examples, the site’s timezone is set to America/New_York (EST-5EDT) and the user is in the America/Los_Angeles (PST-8PDT) timezone.
<ul>
<li>
Local time is in a different year and month from original time: 
 [localize_time]1/1/2014 1:00 am[/localize_time] 
outputs: 
January 1, 2014 1:00 am EST (12/31/2013, 10:00:00 PM PST)
</li>
<li>
Specify a time in timezone different from the site’s: 
 [localize_time tz=”Europe/Paris” ]July 14, 2014 19:00[/localize_time] 
outputs: 
July 14, 2014 7:00 pm CEST (7/14/2014, 10:00:00 AM PDT)
</li>
<li>
Specify a format for the original time: 
 [localize_time fmt=”m/d/Y g:i A T”]June 14, 2014 6:30 AM[/localize_time] 
outputs: 
06/14/2014 6:30 AM EDT (6/14/2014, 3:30:00 AM PDT)
</li>
<li>
Specify a time in the same timezone as the user: 
 [localize_time tz=”PST”]3pm Nov. 1, 2014[/localize_time] 
outputs: 
November 1, 2014 3:00 pm PDT
</li>
</ul>
Note that the display of the local time varies by timezone and browser.

Localize Time

Provides a [localize_time] shortcode, which displays times in the user's local timezone.

Simple default timezone vs Localize Time