// PostsController.php
public function store(PostRequest $request)
{
    $post = Post::create($request->validated());
    
    $post->publish();

    return redirect('/posts');
}

Post extends Model
{
  public function publish()
  {
    $this->published_at = now();
    $this->save();
  }
}

// creating post
$post = Post::create($attributes);

// publish post
$post->published_at = now();
$post->save();