I leave the CO2 24/7.
Yes, it is a waste of CO2 when plants don't need the gas at night.
For cashflow minded persons, that waste of CO2 is nothing compared to the cost of CO2 regulator. The CO2 waste cost will take a long time to get even with regulator cost (10 years?). May be regulator is more economics for LFS owner compared to 1-tank owner.
Of course, ideally, and personally, I prefer regulator. I just want to remind that the 'wasted CO2' must be weighed with the regulator cost. Do not buy regulator yet before you considering all factors (i.e. are you quiting in 5 years time?
Both 24/7 and regulator systems have proven successful. It's up to your judgement.