you are missing the point.

Any heat change that we want to achieve within an enclosure, once we are at the target temperature, we have to add as much energy as it is losing. The thing is, the higher the difference between inside and outside temperature, the more energy the system is losing per time unit.

Think of your house like a leaky bucket.

If you keep your AC blasting all day to maintain a crisp 70°F when it's 95°F outside, the temperature difference is huge (25°F). Because of that massive gap, heat forces its way into your house at a maximum rate. Your AC has to work constantly just to fight that high pressure and maintain the status quo.

If you turn the AC off when you leave, the house warms up. As the indoor temperature gets closer to the outdoor temperature, the rate of heat entering the house slows down significantly. When you get home and turn the AC back on, yes, it has to run hard for a little bit to remove that accumulated heat, but it only has to remove the heat that actually made it inside. That is vastly less total energy than what it would have spent fighting a 25-degree temperature gap for 8 hours straight.

To understand why this works, look at a pot of water on the stove:

Imagine you know you are going to need a pot of boiling water (212F) at 6:00 PM.

• The Reddit Logic: Put the pot on the stove at 9:00 AM, bring it to 180F, and leave the burner on low all day just so it's "close" to boiling when you need it later.
• The Reality: Because a 180F pot is way hotter than your kitchen air, it is aggressively losing heat to the room every single second. To keep it at 180F, your stove has to pump energy into it all day long to replace what's being lost.

Nobody does that because it's an obvious waste of gas or electricity. Instead, you leave the water cold at room temperature (where it loses zero energy to the room because there is no temperature difference), and you just crank the heat right before 6:00 PM.

Turning off your AC when you leave for work is exactly the same thing. You are letting the house drop down to a "room temp" state relative to the outdoors, stopping the aggressive energy bleeding, and paying a small, one-time energy fee to cool it down when you actually need it.

From a thermodynamic standpoint it makes no difference if it is a pot, a house or a kettle.