5 minutes seems rather long, but in those 5 minutes it goes from ~400-550 so it rises ~30ppm/minute. That means that one could detect it within 60 seconds that the CO2 level has rissen, and if well positioned maybe within 30 seconds. WHat is the minimum time you can detect in your graphs? If it is within 1 minute it would be great (OK depends on size of the room etc.
Do you see the same change in temperature - gues not- and humidity - could be? Humans exhale water and CO2 (they are reverse trees :) so those two should change significantly from some average value.
Ideas pop in my mind, like counting people by means of their CO2 output. Fun!