During times of high heat the plant will close its stomata to reduce water loss, no gas exchange will occur. As a horticulture student I wouldn't recommend adding CO2 during high heat as your plants won't be using it, the rubisco might even start consuming the O2 the plant produces during photosynthesis and will deconstruct the glucose it's supposed to be producing. My recommendation would be to turn off the lights and turn on the fans to cool down the space so that the plants don't lockdown their stomata and stop gas exchange. One advantage with Autos is being light independent so they won't get super stressed when you have to turn off lights to help their metabolism.
