skyeriding
901
Ok now I take it back; I don't think its instantaneous - The following vid demonstrates similar classical mechanism of the QP
www.youtube.com
Notice a tiny cam driven continuously (by the cannon pinion/motion works) that lifts the grand lever - that progressively changes the date non-instantaneously. I think this Patek exhibits identical mechanism.
For comparison, the following movement is the 5208 dial side which is of the instantaneous variety. Much more complex than your regular QP with a different grand lever setup - I'd be lying if I said I knew how it works at this point in time!
Regards,
skyeriding