More than a one-off than a big idea, but interesting way to make a time specific promotion.
Having noticed that their sales dropped considerably during lunch hours, emart (self-proclaimed ‘the Walmart of Korea) devised a QR code made of shadows that only works properly from 12 to 1.
During that bracket, the QR code points to short promotions that end past noon and the online purchase gets delivered to the residential address of choice within the day.
Having said that, I’ve recently stumbled upon this site featuring Pictures of People Scanning QR Codes. They should get this one. ;-)