Dogan Ucar

WP Last Modified adds the ‚last_modified_date‘ shortcode to your WordPress installation. This shortcode shows the last timestamp of your post/page. Simply use the „format“ attribute for custom date formats (it uses PHP’s date() function). 
The “description” attribute enables a brief description which changes has been made with the last modification. 
WP Last Modified shows also the actual revision of and the publication date of the post/page. 
You can customize the text which will be shown under each post/page under settings -> WP Last Modified Settings. You can also hide one of the elements if you do not want them.
With version 1.1.0, WP Open Last Modified was renamed to WP Last Modified.
Features:
<ul>
<li>last modification timestamp of a post/page</li>
<li>publication timestamp of a post/page</li>
<li>timestamp format customizable</li>
<li>revision count</li>
<li>custom text with placeholders</li>
<li>last modification description</li>
<li>excluding single posts/pages from displaying the last modification timestamp</li>
</ul>

WP Last Modified

This plugins adds the last modified date, current revision and the publication date of your post/page. Simply use the shortcode [last_modified_date]

Phoenix Online

This plugin allows you to monitor the “Last Modified Time” of up to 20 files, at a glance – right from the WordPress Dashboard.
If you are running regular imports (through <a href="https://wordpress.org/plugins/wp-all-import" rel="ugc">WP All Import</a>, <a href="https://en-gb.wordpress.org/plugins/wordpress-importer/" rel="nofollow ugc">WordPress Importer</a> or similar), this handy tool lets you check on how update your source files are; and is great for diagnosing <code>cron</code> timing mismatches.

File Time Monitor

Running regular imports? This plugin allows you to quickly see when your import / export or other important files were updated!

WP Last Modified vs File Time Monitor