freanki

This widget shows the time since a specific date. You can enter text before and after the result.
You have to enter the date like this: 2012-01-31, so it’s year-month-day.
Thats all 🙂

Time since date

This Plugin provides a widget which shows the days, weeks, month or years since a specific date.

Bill Erickson

Warning This plugin is no longer supported, and does not always work with the Gutenberg block editor.
I recommend using <a href="https://wordpress.org/plugins/change-last-modified-date/" rel="ugc">Change Last Modified Date</a> instead.
<h4>Summary</h4>
Prevent the modified date from changing when making minor changes to your content.
This plugin adds a checkbox to the Publish box, “Don’t update the modified date”. When checked, saving your post does not update the post modified date.
Minor changes like adding tags or fixing typos won’t bump the modified date.
This plugin will maintain the previous modified date. It does not let you specify a custom modified date.
When you’re ready to publish a major content change, you can uncheck this setting before saving the post.
<h4>Customization</h4>
Your theme will need to use <code>get_the_modified_date()</code> to display the modified date.
This plugin only applies to the <code>post</code> post type by default. You can customize which post types it appears on using the <code>limit_modified_date_post_types</code> filter.
<pre><code>add_filter( 'limit_modified_date_post_types', function( $post_types ) {
 $post_types[] = 'page';
 return $post_types;
});
</code></pre>

Limit Modified Date

Prevent the "modified date" from changing when making minor changes to your content.

Time since date vs Limit Modified Date