Good question, outdoors plants are in their vegetative stage in the summer and flowering stage in late summer/fall. Assuming that mimicking nature is the most optimal thing for growth, if anything the vegetative stage should be warmer on average than the flowering stage. There is one member on this forum who is an excellent breeder/grower and I believe he runs CO2, but he runs his canopy at 89-92 during lights on.
This can be difficult to do indoors because if one is vegging in the winter and flowering in the spring, it would be expensive trying to keep temperatures down. It can also depend on the strain and whether or not the plant is a landrace, or native to a certain location and climate.
I believe a good range to shoot for is 70-85 during veg and 65-80 during flower, but wouldn't be too concerned unless the canopy started climbing into the nineties.
Also, it's important to note that atleast a 10-15 degree temperature day/night fluctuation is essential, if plants don't cool down enough at night (or warm up during lights on), they lose the carbohydrates manufactured during the daytime through respiration (this is wasted energy). Given an adequate temperature range, the plant can use those carbohydrates for packing on cell tissue and mass.
