70 to 80 temp activator is exactly that...if the temperature rises above 80 and if it's relatively humid, look for the paint to set up fairly quickly. If it gets to be around 80 to say 83 with little humidity you shouldn't be to bad...but...it will set up faster and your flash times will be affected. A lot depends on how big an area your planning on painting. If it's a complete, you may need to try and get around the car quicker. What can happen and this is usually the problem, if you start say painting at the front clip, by the time you do the fender, one side of the hood, then the other side of the hood and the last fender, the paint on the first fender you just painted may be set up to the point that the paint you put on the door won't melt in and leave you with a dry edge.
Whenever I paint a complete vehicle, I use a reducer and or catalyst that is about 5 to 10 degrees cooler than what the temperature is. I can always wait a little longer for flash times, I can't always paint fast enough to avoid dry spray. Using a slower solvent or catalyst is always a wise choice. You get a better shine, smoother flatter finish and overall better gloss retention.
I wish I had better news for you but paint will react to temperature. The people selling you the product should have made you aware that painting with a slower activator or reducer would lend to getting you a better result, this is one of the joys of buying a technically dependent product from an on line company. If your doing a smaller area, or parts...paint away, you should be fine.
Hope this helps...if not for this case, than for any thing you paint in the future.