No sail past event took place today, and no one is committing to a date. Such an important event is usually well publicized, certainly for a ship that has such a distinguished career. A paying off ceremony usually includes a sail past at HMC Dockyard, for a formal salute, and the ship is dressed and flies a paying off pennant.
The pennant, by Royal Navy tradition, is the length of the ship plus one foot per year of service.
By my strictly unofficial calculation, that would make a pennant of 426 ft plus 42 ft (if the date of the ship's first commission is used) = 468 feet.
Although I do not know if the RCN has ever done this, some navies have used balloons to fly the long pennant.