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 68 to 72 F temperature is likely more for the wintertime when you have the heat on, as that would typically be a little cold in the summer when you have the air-conditioner on. A temperature of 75 to 78 F would be more sensible in the summer and more environmentally friendly.