Harry, a fully worked example of what you are proposing has been posted here in the recent past with a modern fridge freezer as the reference (using manufacturers quoted annual kWh figures)
With 25 million of them in use it leads to just 500MW of load saving so almost completely irrelevant with peak demands of 40 - 60GW
A fridge freezer will also have issues with interruptions of many hours particularly during periods when access is required and there are no other domestic appliances that lend themselves to interruptions at or around the peak.