Two different issues are being discussed in this thread. First is the siesta light question, second involves the effect of CO2.
On the CO2 first. What makes you think you need it? There is quite a lot of CO2 occurring naturally in a planted aquarium. We tend to think of fish producing the CO2, but the fact is that more CO2 comes from the bacteria in the substrate, filter, everywhere than from the fish. And I am not meaning only the nitrification bacteria, there is a huge array of bacteria in the substrate.
There has to be a balance between light and nutrients, and the nutrients themselves have to be in balance for what plants require. Increasing one, like carbon (CO2) is going to tip the existing balance (assuming there is one, I don't know the state of your aquarium) and mean increasing other components to re-establish a new balance. And the higher the additives, the more something can go wrong to bring it all down.
As for the light siesta, this is generally believed to have some impact on algae. But here again, messing with photo periods is going to have some effect on the fish and the plants. No one has yet assessed the impact on fish. The authors who endorse this method believe plants are not affected. I am not convinced.
This method of a mid-day siesta was raised on a plant forum by Diana Walstad as beneficial. Tom Barr's response was that it was unlikely to be worth anything. I agree with his assessment that if algae is a problem, you have too much light for the nutrients. That is easily resolved, and without possible risk to fish and plants.
Natural planted tanks are supposed to be just that--natural, using nature rather than paraphernalia to do the work.