Yo Ho yeroc1982,
Your very right about wanting to keep the temps around 76-78* degrees, but you are not really in the danger zone with daytime temps that might climb to 85* degrees. You need to watch the watering, and make certain you are not crisping any leaves. This wonderful plant endures temps that vary since it does grow all over the planet, obviously it isn't going to grow in sub-zero temps, but in the tropics it sure gets hotter than 85*.
Ed Rosenthal's Grow Tips
Maintaining Optimum Grow Room Temperature
Marijuana plants are very hardy and survive over a wide range of temperatures. They can withstand extremely hot weather - up to 120 degrees - as long as they have adequate supplies of water. Cannabis seedlings regularly survive light frost at the beginning of the season.
Both excessively high and low temperatures can slow marijuana's rate of metabolism and growth. The plants function best in moderate temperatures - between 60 and 85 degrees. As more light is made available, the ideal temperature for normal plant growth increases. In high temperature and moderate light conditions, the plant's stems elongate. Strong light and low temperature conditions will decrease stem elongation. During periods of low light, stem elongation can be decreased by lowering the temperature.
Like I said just be watchful.
smoke in peace
KingKahuuna