We have a CO2 monitor to keep track of CO2 concentrations indoor during the dreadful time of the year we can't always keep windows open. It's very useful and gives off an alarm if CO2 levels exceed 800ppm or twice the natural background level so we can let in fresh air.

Now the interesting thing is that CO2 increase varies strongly and it took us a while to find out why. Sometimes values would barely increase in hours, on other days you could watch them climb up within minutes. We knew wasn't host or the cats as they're always around but it was something totally unexpected - our house plants, or rather the soil they're in. The microbial community in the soil produces loads of CO2, but only if it's moist enough. So when the plants are dry not much is going on but after watering them, CO2 levels shoot up because the microbes in the soil turn up their metabolism. It far exceeds CO2 uptake by photosynthesis which is zero at night for most plants anyway. But that's another story.

TL;DR
Many people think house plants will improve their air quality but in fact they can suck away your oxygen rather than produce it for you unless it's really bright and warm.