For a few years now I have kept my light on for 12 hours a day.
However, I have always turned it on in the morning 6am to 12 noon and
then again in the evening 6pm to 12 midnight. I kept it off during the
day because of how hot the tank gets in the summer.

I never seemed to have a problem with this setup, but now am wondering
if its not such a great idea. Should I instead put the light on for 12
hours continuously? Say from 11 am to 11 pm ? Is there a difference
for the plants in processing CO2 and O2 ?

Much thanks