Codstack

<a href="http://www.youtube.com/watch?v=T_J67i9yKr8" rel="nofollow ugc">Demo</a> 
This wordpress plugin enables you to have a dynamic sidebar in a way that you can post automatically in there. By this plugin you can add and remove your widgets automatically. You set your Start Date and End Date in the plugin and everything will be done for you! For instance you want to insert a banner or advertisement for the coming new year but you can not do it just at the exact coming new year time! So whenever you have time you can set a future Start Date and an End Date in this plugin and everything is just done with that! The plugin itself inserts your banner at the given Start Date and End Date. For another example you can make a deadline for your banner by just giving an End Date in the plugin and the banner starts but will be removed on the End Date automatically.
There are three different ways:
1) Manually
It is just like HTML Text Widget but you can use Twitter Bootstrap Classes, access to Media Library and insert links and images easily and quickly.
2) Automatically
Rather than all of the features in “Manually” you can set a Start Date and an End Date for your widget so your widget will be shown on your website at your Start Date that you have just set and will be removed at End Date that you have just set. NOTE: If you want to use this type you must have another active widget ( with any type ) in your sidebar.
3) Deadline
Beside all of the features in “Manually” type, there is an End Date that you can set and when you active this type of widget it will be shown in your sidebar and whenever it reaches to its End Date it will be removed from your website automatically.
Automatic Widgets Meta Box ( in WordPress Dashboard menu )
Here you can view all of your “automatically and deadline” widget types. You can see when they are started or ended. For instance you can see which “automatically” types are going to be started or which “deadline” types are going to be removed form your sidebar. It is actually your statistics of automatic widgets.
We hope you like it, thank you very much indeed.

wp_automatic_widget

This wordpress plugin enables you to have a dynamic sidebar in a way that you can post automatically in there.

Themezly

<blockquote>
Did you find this plugin helpful? Please consider <a href="https://wordpress.org/support/plugin/assign-widgets/reviews/" rel="ugc">leaving a 5-star review</a>.
</blockquote>
Assign Widgets plugin for WordPress will help you assign widgets to specific pages or create custom widget areas. Plugin options are located under every WordPress widget area and they will let you control widgets visibility.
<a href="http://creatus.io/" rel="nofollow ugc">Sponsored by: Creatus.io</a>
<div class="embed-vimeo" style="text-align: center;"><iframe loading="lazy" src="https://player.vimeo.com/video/302173904" width="750" height="422" frameborder="0" webkitallowfullscreen mozallowfullscreen allowfullscreen></iframe></div>
Get involved 
Developers can contribute to the source code on the <a href="https://github.com/Themezly/Assign-Widgets" rel="nofollow ugc">Assign Widgets GitHub Repository</a>.
<h4>Minimum Requirements</h4>
<ul>
<li>WordPress 4.0 or greater</li>
<li>PHP version 5.6 or greater</li>
</ul>
<h4>Installation</h4>
<ol>
<li>Upload <code>Assign-widgets-version_number.zip</code> to the <code>/wp-content/plugins/</code> directory and extract.</li>
<li>Activate the plugin by going to Plugins page in WordPress admin and clicking on Activate link.</li>
<li>Go to the Widgets admin page and open the accordion from the widget that you want to assign.</li>
<li>Select Hide on selected pages/types or Show only on selected pages/types than from Assigned pages or view types select the assignment pages.</li>
</ol>

Assign Widgets

A simple and easy way to assign widgets to a specific page or create widget area.

wp_automatic_widget vs Assign Widgets