It does work, though. Nest's program pre-cools to get you through the hottest hours without having to kick on the AC, moving some of the region's demand from the 4-6pm slot to the 2-4pm slot.
I find myself going "huh, it's getting a little warm" at about 5:45pm, at which point I check and remember it's a "Rush Hour" session.
Does precooking really work? I’d assume it would have to cool my house down below 65 to keep it below 80 all afternoon. 111+ days are brutal in certain rooms even with both ACs set to 76.
The last 30 years have been a renaissance of insulation and energy efficiency. Pre cooling, fan recirculation, humidity consideration, time of use observance may only delay/reduce a few cycles per house per day, but in aggregate, that's significant.
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.
Depends on the shape of the temperature graph for the day, the power of your AC system, your insulation, etc.
If your on a day that doesn't get below 90 and gets above 110 during the hottest part of the day and your AC is barely rated at the minimum recommended for your square footage and you have average insulation, no, and even regular AC use is going to be marginal and your AC is probably going to frequent service.
(And the things that make precooling work better also will make your AC work better and, for the most part, more energy and maintenance cost efficiently when you aren't precooling.)
If you live in a place where you frequently need AC, aside from decent insulation, getting an overrated, high-efficiency unit (which seem to be correlated for residential units, probably because both drive up cost, and there is a correlation between people looking for more capacity and people concerned with efficiency) is a serious quality of life improvement.
Does for me. Around 7 PM, my AC kicks on to drop the house a few degrees; sun's down low and air temperature has been dropping by then.
Later in the evening, it drops lower to be able to sleep, but also cool down the house, and taking advantage of the coolest part of the day for best efficiency of the AC system. It stops holding that temperature around 7-8am and goes to a much higher set point.
The house stays dry enough through the day that it never really gets uncomfortable, especially with a gentle breeze from a small, quiet fan in the room.
I would not expect this sort of solution to be super useful in a place that gets 111 degree days, where AC is literally keeping folks alive. You'd probably get more benefits from a housing code that requires extended roofs for shade, light colored exteriors, etc.
I find myself going "huh, it's getting a little warm" at about 5:45pm, at which point I check and remember it's a "Rush Hour" session.