I can't speak for the specifics of using a Nest, but pre-cooling a house earlier in the day is definitely a more efficient use of power. Earlier in the year in

I can't speak for the specifics of using a Nest, but pre-cooling a house earlier in the day is definitely a more efficient use of power. Earlier in the year in Australia when day time temperatures were 35°C-40°C (95°F-104°F), waiting until midday to turn on the AC would mean using another 10 kwh more than if the AC was turned on at 9am. Granted, this is an new Australian house which means it's built to standards about 30 years behind what you would expect for a first world country.