Here in MN in July, there is a 20 degree difference between the daytime high and evening low. Why not turn off the A/C during when you go to bed and let the evening breeze push in cooler air that is probably cooler than what you have your central air set to. You could also stick a box fan in the window to help bring in more cool air and help circulate it more around the room (also, have those ceiling fans turned on to help circulate the air.)
Once it starts to warm up in the morning, be sure to take those fans out of the window so that you are not circulating in warm air. You might even consider closing the windows if it starts warming up. As long as your home is sufficiently insulated and you are not coming & going a lot & you keep shades drawn, you can help keep the temperature down in your home without having to turn on the central air.