Ravi Kiran Katha

WordPress has a site-level timezone setting configured from the admin back-end. All dates and times displayed on the front-end are typically displayed in this timezone.
This plugin enables the display of dates/times in the front-end using the browser’s timezone. This is done by overriding the WordPress’s ‘timezone_string’ and ‘gmt_offset’ options to match the user’s timezone for the duration of a particular request 
ONLY on the front-end interface.
<h4>Browser Timezone Detection</h4>
The browser’s timezone is detected using one of the following two methods
<ol>
<li><a href="http://pellepim.bitbucket.org/jstz/" rel="nofollow ugc">jsTimezoneDetect</a> (default)</li>
<li><a href="http://caniuse.com/geolocation" rel="nofollow ugc">HTML5 Geolocation API</a> and <a href="https://developers.google.com/maps/documentation/timezone" rel="nofollow ugc">Google Timezone API</a></li>
</ol>
jsTimezoneDetect (default) 
 This is the default timezone detection mechanism. Please refer to the script <a href="http://pellepim.bitbucket.org/jstz/" rel="nofollow ugc">home page</a> 
for the compatibility and other notes
HTML5 Geolocation API 
 Detects the current geo-location using <a href="http://caniuse.com/geolocation" rel="nofollow ugc">navigator.geolocation.getCurrentPosition</a>. The location thus detected will be sent to the <a href="https://developers.google.com/maps/documentation/timezone" rel="nofollow ugc">Google Timezone API</a> 
which returns the timezone id – similar to “Asia/Kolkata”.
This method requires you to
<ul>
<li>Enable the “Google Timezone API” option on the plugin options page</li>
<li>Specify a valid <a href="https://developers.google.com/maps/documentation/timezone/get-api-key" rel="nofollow ugc">Google API Key</a>
<ul>
<li>The key should be a browser key</li>
<li>The “Accepted HTTP Referrers” should include the domain name used by the hosting wordpress site or left blank to allow all referrers</li>
</ul>
</li>
</ul>
If the required options for the usage of Google Timezone API are not met, the detection mechanism falls back to the default one.
<h4>Post Timezone Detection</h4>
<ul>
<li>If the browser’s timezone id is not detected successfully, everything else behaves as if this plugin is not installed.</li>
<li>If the browser’s timezone id is detected, the following actions take place
<ul>
<li>A cookie will be set in the browser, based on the cookie options specified on the plugin options page</li>
<li>If a cookie already exists previously with the same id, no action is taken</li>
<li>If a cookie doesn’t already exist previously or exists with a different timezone id, then a window.reload is triggered to refresh the page so that the dates/times on the page are updated</li>
</ul>
</li>
</ul>
<h4>EventON Hook</h4>
This plugin provides a feature to hook into the EventON plugin. When enabled, all EventON dates/times are updated to reflect the browser’s timezone.
<h4>Shortcodes</h4>
This plugin defines the below shortcodes
<ol>
<li>[wp_user_timezone_id] => Returns the timezone id of the browser or null if not available.</li>
<li>[wp_user_timezone_offset] => Returns the timezone’s gmt offset in hours of the browser or null if not available.</li>
</ol>
<h4>Options</h4>
This plugin defines the below options to retrieve the original timezone_string and gmt_offset defined at the site level
<ol>
<li>get_option( ‘site_timezone_string’ ) => Returns the original timezone_string option for the site</li>
<li>get_option( ‘site_gmt_offset’ ) => Returns the original gmt_offset option for the site</li>
</ol>
<h4>Actions/Hooks</h4>
This plugin defines the below filters/hooks
<ol>
<li>apply_filters( ‘wp_user_timezone_id’, $tz_id ) => Allows you to override the timezone string determined by the plugin. This filter can be used to apply user’s timezone preference. If any plugin or wordpress core implements a feature to accept and store user’s preferred timezone, the ‘wp_user_timezone_id’ can be used to apply that timezone value to the front-end. Reference: <a href="https://core.trac.wordpress.org/ticket/18146" rel="nofollow ugc">Add user-level timezone setting</a>).</li>
</ol>
<h4>Admin Backend Dates/Times</h4>
Important: The admin back-end is not modified by this plugin. All dates/times displayed in the back-end are still in the original timezone specified by the WordPress General Settings.

WP User Timezone

Magnificent

WP User Timezone displays the front-end dates & times in the browser's local timezone without actually modifying your database.

Bernhard Riedl

<ul>
<li>based on PHP timezones database (please read the <a href="https://wordpress.org/plugins/timezonecalculator/faq/" rel="ugc">FAQ</a> for further information)</li>
<li>fully settings page configurable with GUI or manually</li>
<li>easy to integrate (ships with multi/sidebar- and dashboard-widget functionality)</li>
<li>display clock in WordPress Admin Bar</li>
<li>possible to integrate in “Right Now” box or to display as widget on the dashboard and on the user’s profile page</li>
<li>Calculator section in Tools-Menu with individual timezone-selection for every user</li>
<li>optional Ajax refresh with jQuery</li>
<li>fully compatible with <a href="https://codex.wordpress.org/Administration_Over_SSL" rel="nofollow ugc">https/SSL/TLS-sites</a></li>
<li><a href="https://wordpress.org/plugins/timezonecalculator/other_notes/" rel="ugc">API for developers</a></li>
<li>fully multisite network compatible</li>
<li>clean uninstall</li>
</ul>
Plan your travels with the free <a href="https://www.journeycalculator.com/" rel="nofollow ugc">JourneyCalculator</a> which is based on TimeZoneCalculator.
Please find the version for WordPress
<ul>
<li>3.8 and higher <a href="https://downloads.wordpress.org/plugin/timezonecalculator.zip" rel="nofollow ugc">here</a></li>
<li>3.3 to 3.7 <a href="https://downloads.wordpress.org/plugin/timezonecalculator.wordpress3.3-3.7.zip" rel="nofollow ugc">here</a></li>
<li>2.8 to 3.2 <a href="https://downloads.wordpress.org/plugin/timezonecalculator.wordpress2.8-3.2.zip" rel="nofollow ugc">here</a></li>
<li>1.5 to 2.7 <a href="https://downloads.wordpress.org/plugin/timezonecalculator.wordpress1.5-2.7.zip" rel="nofollow ugc">here</a></li>
</ul>
Plugin’s website: <a href="https://www.bernhard-riedl.com/projects/" rel="nofollow ugc">https://www.bernhard-riedl.com/projects/</a>
Author’s website: <a href="https://www.bernhard-riedl.com/" rel="nofollow ugc">https://www.bernhard-riedl.com/</a> 
Attention! – Geeks’ stuff ahead! 😉
<h4>API</h4>
With TimeZoneCalculator 2.00 and higher you can also realize a html select which displays for example the airtime of your internet radio station or your broadcasts in your users’ local time. Another possibility for the usage of the upcoming function is the integration of date, time and timezone information into your travelling blog.
Parameters can either be passed <a href="https://codex.wordpress.org/Function_Reference/wp_parse_args" rel="nofollow ugc">as an array or a URL query type string (e.g. “display=0&format=0”)</a>. Please note that WordPress parses all arguments as strings, thus booleans have to be 0 or 1 if used in query type strings whereas for arrays <a href="https://secure.php.net/manual/en/language.types.boolean.php" rel="nofollow ugc">real booleans</a> should be used. – Furthermore you have to break your timezones with \n : <code>America/New_York;EST;EWT;New York, NY, US;New York, NY, US;0;0\nEurope/Vienna;;;sleep longer in winter;get up earlier to enjoy the sun;1;0</code> if you want to use different timezones in a query_string. In case you use an array, an array should also be used for the timezones.
<code>function $timezonecalculator->output($params=array())</code>
$params:
<ul>
<li>
<code>query_time</code>: any unix timestamp (where <code>-1262304000 <= query_time <= 2145916800</code>) or any English textual datetime description in the range of <code>1930-01-01</code> and <code>2038-01-01</code> which can be parsed with <a href="https://secure.php.net/manual/en/function.strtotime.php" rel="nofollow ugc">PHP’s strtotime function</a>; default is set to current UTC
</li>
<li>
<code>query_timezone</code>: origin-timezone of <code>query_time</code>; you can choose a <a href="https://secure.php.net/manual/en/timezones.php" rel="nofollow ugc">PHP timezone_string</a>; otherwise <code>UTC</code> will be used
</li>
<li>
<code>before_list</code>: default <code><ul></code>
</li>
<li>
<code>after_list</code>: default <code></ul></code>
</li>
<li>
<code>format_timezone</code>: default <code><li><abbr title="%name">%abbreviation</abbr>: %datetime</li></code>
</li>
<li>
<code>format_datetime</code>: default <code>Y-m-d H:i</code>
</li>
<li>
<code>timezones</code>: alternative timezones-array – each array entry has to be a string as described in the Manual Selection Section of the Admin Menu; default is the timezones-entries array which can be modified in the Admin Menu
</li>
<li>
<code>prefer_user_timezones</code>: prefer user set timezones – if they exist – to global or function call timezones; default is <code>false</code>
</li>
<li>
<code>user_id</code>: determines which user’s timezones should be used; not set as default -> use the timezones of the user who is currently logged in
</li>
<li>
<code>use_container</code>: if set to <code>true</code> (default value), the current UTC is used as <code>query_time</code> and the same selected timezones and format is used as set in the admin menu, TimeZoneCalculator wraps the output in a html div with the class <code>timezonecalculator-refreshable-output</code> – the class <code>timezonecalculator-output</code> will be used for all other output; if you set <code>use_container</code> to <code>false</code>, no container div will be generated
</li>
<li>
<code>display</code>: if you want to return the timezone-information (e.g. for storing in a variable) instead of echoing it with this function-call, set this to <code>false</code>; default setting is <code>true</code>
</li>
<li>
<code>format_container</code>: This option can be used to format the <code>div</code> container with css. Please note, that it should only be used to provide individual formats in case the class-style itself cannot be changed.
</li>
<li>
<code>no_refresh</code>: If set to true, TimeZoneCalculator will not produce any Ajax-Refresh-code, even if you have enabled the Ajax refresh in the admin menu.
</li>
</ul>
Example for including a world-clock in your <a href="https://codex.wordpress.org/Theme_Development" rel="nofollow ugc">post-template</a> (usually single.php or post.php in wp-content/themes) using <a href="https://codex.wordpress.org/Template_Tags/the_date" rel="nofollow ugc">WordPress the_date() function</a>:
Find something similar to
<pre><code>the_date();
</code></pre>
or
<pre><code>the_time();
</code></pre>
and replace it with
<pre><code><?php $timezonecalculator->output(array('query_time' => the_date('U', '', '', false))); ?>
</code></pre>
This outputs your selected timezones, whereas calculations are based on the timestamp of your post instead of using the current UTC.
<h4>Shortcodes</h4>
<a href="https://codex.wordpress.org/Shortcode_API" rel="nofollow ugc">How-to for shortcodes</a>
General Example:
Enter the following text anywhere in a post or page to inform the clan when to meet up again:
<pre><code>let's meet tomorrow for a new challenge at:

[timezonecalculator_output query_time="tomorrow 8pm" query_timezone="Europe/Vienna" timezones="Europe/Vienna\nAsia/Bangkok"]
</code></pre>
Available Shortcode:
<pre><code>timezonecalculator_output
</code></pre>
Invokes <code>$timezonecalculator->output($params)</code>. Please note that you have to use a query_string to select timezones which can be parsed into an associative array. – For example: <code>America/New_York;EST;EWT;New York, NY, US;New York, NY, US;0;0\nEurope/Vienna;;;sleep longer in winter;get up earlier to enjoy the sun;1;0</code>
<h4>Filters</h4>
<a href="https://codex.wordpress.org/Function_Reference/add_filter" rel="nofollow ugc">How-To for filters</a>
Available Filters:
<pre><code>timezonecalculator_defaults
</code></pre>
In case you want to set the default parameters globally rather than handing them over on every function call, you can add the <a href="https://codex.wordpress.org/Function_Reference/add_filter" rel="nofollow ugc">filter</a> <code>timezonecalculator_defaults</code> in for example timezonecalculator.php or your <a href="https://codex.wordpress.org/Writing_a_Plugin" rel="nofollow ugc">own customization plugin</a> (recommended).
Please note that parameters which you hand over to a function call (<code>$timezonecalculator->output</code>) will always override the defaults parameters, even if they have been set by a filter or in the admin menu.
<pre><code>timezonecalculator_dashboard_widget
</code></pre>
Receives an array which is used for the dashboard-widget-function call to <code>$timezonecalculator->output($params)</code>. <code>display</code> and <code>use_container</code> will automatically be set to true.
<pre><code>timezonecalculator_dashboard_right_now
</code></pre>
Receives an array which is used for the right-now-box-function call to <code>$timezonecalculator->output($params)</code>. <code>display</code> and <code>use_container</code> will automatically be set to true.
<pre><code>timezonecalculator_world_clock_tools_page
</code></pre>
Receives an array which is used for the world-clock-function call on the tools-page to <code>$timezonecalculator->output($params)</code>. <code>display</code>, <code>use_container</code> and <code>prefer_user_timezones</code> will automatically be set to true.
<pre><code>timezonecalculator_user_profile
</code></pre>
Receives an array which is used for the user-profile-function call to <code>$timezonecalculator->output($params)</code>. <code>display</code>, <code>use_container</code> and <code>prefer_user_timezones</code> will automatically be set to true.
<pre><code>timezonecalculator_admin_bar_clock
</code></pre>
Receives an array which is used for the admin-bar-clock-function call to <code>$timezonecalculator->output($params)</code>. <code>display</code> will automatically be set to false and <code>use_container</code> to true. Moreover, the <code>timezones</code> will be set to Local_WordPress_Time. The filter <code>timezonecalculator_admin_bar_clock_format_container</code> will be used as default format for the clock.
<pre><code>timezonecalculator_admin_bar_clock_format_container
</code></pre>
Receives a string which represents the container style.
<pre><code>timezonecalculator_admin_bar_clock_position
</code></pre>
Position of the clock in the Admin Bar (see <code>wp-includes/class-wp-admin-bar.php</code> function <code>add_menus</code>). Default is <code>1000</code> which is the last position.
<pre><code>timezonecalculator_calculator
</code></pre>
Receives an array which is used for the calculator-page function call to <code>$timezonecalculator->output($params)</code>. <code>display</code>, <code>use_container</code> will automatically be set to true.
<pre><code>timezonecalculator_calculator_timezone
</code></pre>
Receives a timezone-string which is used for the calculator-page.
<pre><code>timezonecalculator_calculator_format_date
</code></pre>
Receives an array whereas each entry represents a date-format. The first date-format will be used as display-format in the textfield.
<pre><code>timezonecalculator_calculator_format_time
</code></pre>
Receives a string which is used to determine whether to use 12 or 24-hour clock. In case this string contains <code>a</code> or <code>A</code>, the 12-hour clock will be preferred.

TimeZoneCalculator

Calculates, displays and automatically updates times and dates in different timezones with respect to daylight saving.

WP User Timezone vs TimeZoneCalculator