What to expect
The water of Laguna 69 is the familiar final image, but the trek is the visit. SERNANP describes the route via Cebollapampa. If your main interest is seeing lakes, investigate the separate options around Chinancocha and Orconcocha. That is a different plan, not a failed Laguna 69 visit.
How it fits into a journey
Keep the whole day free, including outward and return travel. Do not automatically schedule Laguna 69 straight after your bus arrival or treat a number of nights in Huaraz as proof you are ready.