Just curious whats the purpose of venting the room after the light cycle and is this necessary? I am working to upgrade to a sealed room with CO2 also but didn't have any plans to vent the room other when I open the door to go in and out. Also mine will probably not be quite as sealed as your kick ass clean room setup its just a 10x10 spare bedroom im gonna seal up best I can
If you don't have Co2, the air should exchange constantly, or at least every 20 minutes.
In my set-up, Co2 turns on with the lights and the venting/airexhange stops. When lights go out, the room exchanges every 3 minutes, with hepafiltered air in, and charcoal filtered air out. It smells fresh and clean.