Update existing posts to random publication dates

gistfile1.txt

  $posts = get_posts(
    array(
      'numberposts' => -1,
      'post_status' => 'any',
      'post_type'   => 'post' //you can use a cpt
    )
  );
  foreach( $posts as $post ) {

    //Generate a random date between 1 May 2017 and now
    $random_date = mt_rand( strtotime( '1 May 2017' ), time() );
    $date_format = 'Y-m-d H:i:s';
    $post_date = date( $date_format, $random_date );
    
    //Update the post
    $update = array(
      'ID' => $post->ID,
      'post_date' => $post_date,
      'post_date_gmt' => null,
    );
    wp_update_post( $update );

  }