Seth Yoder

When you password-protect a post in WordPress, a cookie is set to expire in 10 
days which prevents the user from having to enter the password during that 
10-day period. This plugin allows you to easily change the lifetime of that 
cookie.

Password Protection Expiration

Allows you to easily change the lifetime of the WordPress cookie which allows automatic login to password-protected posts.

kuck1u

VisuAlive

VA Simple Expires is a plugin that allows you to add an expiration date to posts. 
The usage is pretty simple. You define an expiration date to a post and when the date comes, the post is removed from the public side of your site and set to “expiration”. “Expiration” is a new post status added by the plugin.
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VA Simple Expires

This is the fork of Simple Expires created by Mr. abmcr. Simple plugin which can set up the term of validity.

Password Protection Expiration vs VA Simple Expires