Another thing to remember is the humidity levels. During this period, dendrobiums do not need a lot of moisture. Very little water will be enough to keep their roots alive. Also keep in mind that their roots constantly need plenty of air circulation so you should place them where there is a lot of fresh air.
Remember, that is based on energy usage, not comfort-levels, which are the purpose of having an air conditioner, in my not-so-humble opinion. Fact: At night, the ideal temperature comfort range for Americans drops to 65 to 72 degrees Fahrenheit (or about 87 degrees if you are my wife).
The difference in where you set the thermostat only affects how much cold air it blows into the room. The lower temperature at which you set the thermostat in summer, the more air it blows in. Setting the thermostat at 78 degrees typically keeps enough cool air in the room for comfort. Unless you developed a keen temperature sensitivity, you won't likely notice the difference between 73 degrees and 78 degrees.