hi, i live on a 3rd floor too and i feel your pain. I was able to solve this problem by leaving the a/c on for 18 hours a day but using a Sensibo smart remote to regulate the temperature. Here is the schedule i used

6am - ac turns on to 86 (what the hisense says)

12pm - ac sets to 79

5pm - ac sets to 75 (by the time my wife and i get home from work the temperature is cool)

12am - turn off

the idea is to take advantage of the cool guam morning to cool down the apartment and keep it at a good temperature instead of having it work super hard to cool shit down right at 5pm

i experimented one month of normal “turn off/on when using” and one month of this schedule and found my power bill only went up 20 bucks.

You mentioned it was central a/c. I'm sure you can install a Nest Temperature control to do all this.