Why not use a simple timer for the AC? Do you come home at different times each day?
A timer also can't tell me if my AC is actually on, may fail in the case of a power outage or I may forget to set it, as such using a timer doesn't provide a meaningful improvement over just turning on the AC when I get home and tolerating the heat for half and hour or so.
In the end, a timer has no feedback, so a closed loop system will always be better. I've been burned numerous times by open-loop systems in home automation, so I don't do that anymore. That's the second reason why I spend a lot more effort and money on sensors rather than actuators (the first reason being that graphs are fun).
Given that the load is likely removing peak daytime heat, then sustaining a less-challenging night-time temperature, the net impact is probably even less.
It's not horrible, but that's like half a space heater and most people spring for something bigger.
First hour use may approach peak, but again, most of that is incurred regardless.
5 kWh is $0.50 - $1.00, which is the cost of running an hour long for a day, the worst-case scenario. You'd spend a lot more on IoT kit (the Turris Omnia alone is $300) for minimising that cost.
Timers are cheap.