问题

答案很简单。我所做的是创建一个插件，激活后获取所有帖子，循环浏览，生成一个随机日期，并用该日期更新帖子。

<?php
/**
 * Plugin Name: WPSE 259750 Random Dates
 * Description: On activation, change the dates of all posts to random dates
 */

//* We want to do this only once, so add hook to plugin activation
register_activation_hook( __FILE__ , \'wpse_259750_activation\' );
function wpse_259750_activation() {

  //* Get all the posts
  $posts = get_posts( array( \'numberposts\' => -1, \'post_status\' => \'any\' ) );
  foreach( $posts as $post ) {

    //* Generate a random date between January 1st, 2015 and now
    $random_date = mt_rand( strtotime( \'1 January 2015\' ), time() );
    $date_format = \'Y-m-d H:i:s\';

    //* Format the date that WordPress likes
    $post_date = date( $date_format, $random_date );

    //* We only want to update the post date
    $update = array(
      \'ID\' => $post->ID,
      \'post_date\' => $post_date,
      \'post_date_gmt\' => null,
    );

    //* Update the post
    wp_update_post( $update );
  }
}