I have no intent to draw comparison with Walstad method as I understand the two setups are heaven and earth different.
I understand having shorter photo period is to control algae in high light systems. But I have low/medium light, not substantially different from Amano Nature aquariums that are between 35 to 50 PAR from Tom Barr's measurements.
Yes, with CO2, low light plants will grow faster, but only relative to non-CO2 condition and still much slower than fast growing plants. The benefit of faster growth in slow growing plants is to outgrow algae, which I have not found the growth fast enough in low light CO2 system.
Another benefit of having a longer photo period is for me. I prefer longer viewing time of my tank than leave it in darkness most of the day. Similarly, split photo periods give me more viewing time in the morning and evening when I am home, and hopefully promote faster plant growth and less algae by splitting long photo period.
I post this to explore the pros and cons of having longer photo period, and split photo periods, in low light CO2 system, and hopefully get feed back from people who have tried it.