Right now, my whole house AC isn't working, so I just have one window unit, and I let it run all day. If they get hot, they know what room is the coolest.
Also, you want to keep your house at a modestly cooler temp in the summer, because as far as energy used, you're still gonna suck up a lot of juice trying to cool off your hotter house when you get home from work. If you don't have central air, I would recommend a window one, and just keep one room nice for your fur buddy. You can also get a standup fan and suck air out of there into the rest of the house, and spread it out a little for yourself as well, instead of just chilling one room.
I usually set my programmed one for 75-78 during the day. Warmer than that, and the dogs would melt, and all my houseplants would be pissed.