With your system you leave it running 24/7 for a week and the replace the mix. Don't use the supplied sachets, use the pinned article which explains a sugar/yeast/water mix which is 100x better than those silly sachets. If you were to disconnect the pipe each night oyu would lose the pressure, let the mix gas off and it would be a waste of time.
You are correct in thinking that in the photoperiod plants take in CO2 and not at night. However this doesn't apply to your setup. DIY is almost impossible to overdose with and if you are worried then set an airstone on a timer to drive away the CO2 at night.
Some of us with pressurised use solenoids to only inject CO2 during the day and others run it 24/7. Remember in nature there is no on/off tap but it also isn't an enclosed glass box that we have control over!!!