My suggestion would be to use it about 10 minutes after the lights first come on....then maybe every hour or two that they are on, have the fans go off on a timer, then have CO2 come on and let it sit with the fans off for a good 15 minutes each time....you would just have to be careful about not letting tops of the plants burn by being too close to the lights when the fans are off for the short 15 minute enrichment....but in all reality i think you are going to find that this is more trouble than it is worth. CO2 enrichment is best left for the HPS setups that are in sealed rooms with AC units or whatever you need to keep temps below 85. Because in this type of setup, your room is constantly at the correct CO2 enrichment PPM level, whereas with what you are trying to do, its gonna be CO2 at a high PPM for a few minutes, then clear all the CO2 out in order to keep things cool, just wasting it...I don't even try CO2 enrichment in my tent anymore just because I found that having an intake fan and exhaust fan works just about as good since plants are getting constant fresh air.