There are a lot of variables in this question. You will always save money if you turn your air conditioner off or put it on a higher temperature setting while you’re not in the room. However, with many Room ACs, unlike central air conditioning, you can’t program it to go on at a certain time, so when you come home you will have to set it to the desired temperature and depending on the unit, the outside temperature, and your insulation, it will take a certain amount of time to reach that desired temperature. Another option is to use a programmable wall outlet timer with your room AC. Make sure that the amperage and voltage ratings of the wall outlet timer are appropriate for the electricity demands of the room air conditioner.
If you have a separate Room AC in your bedroom, it might work to turn that off while you are out, and turn it back on when you return and by the time you’re ready to retire to your bedroom it will be cooled off.
If you are purchasing a new room air conditioner, you may want to look for one with a built-in timer and/or programmable thermostat settings.
For more tips on how to stay cool this summer, visit: energystar.gov/home.
All of this information is courtesy of Energy Star.