PMPro Customizations to allow non-members to view specified restricted posts if they are less than a specified amount of days old for that specific post.

open_specific_new_posts_to_non_members_with_set_date.php

<?php
/**
 * This recipe allows non-members to view specific restricted posts
 * if they are less than the amount of days specified per post old.
 *
 * To set which posts to unlock and their individual period (days)
 * set the post id's as the array key and the period as the
 * value of the array key of the $posts_to_unlock variable.
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function open_specified_new_posts_per_date_to_non_members( $hasaccess, $thepost, $theuser, $post_membership_levels ) {

	// Set your post id's and the unlock period here.
	$posts_to_unlock = array(
		2   => '-30 Days', // post ID 2, less than 30 days old
		35  => '-45 Days', // post ID 35, less than 45 days old
		155 => '-14 Days', // post ID 155, less than 14 days old
	);

	global $wpdb;

	//if PMPro says true already, return true
	if ( $hasaccess ) {
		return $hasaccess;
	}

	//figure out dates to check
	$thepost_id = $thepost->ID;
	$cutoff     = strtotime( $posts_to_unlock[ $thepost_id ], current_time( 'timestamp' ) );
	$published  = strtotime( $thepost->post_date, current_time( 'timestamp' ) );

	//if published after the cuttoff, then allow access for now
	if ( $published > $cutoff && array_key_exists( $thepost_id, $posts_to_unlock ) ) {
		$hasaccess = true;
	}

	return $hasaccess;
}
add_filter( 'pmpro_has_membership_access_filter', 'open_specified_new_posts_per_date_to_non_members', 10, 4 );

This recipe is included in the blog post on "Lock or Unlock Posts Based on Age and Post Date" at Paid Memberships Pro here: https://www.paidmembershipspro.com/lock-unlock-posts-based-age-post-date/