How would he plan on dispersing the c02?

Does he run 24/0 or 18/6 Veg? (yes, it does matter when c02 is concerned)

As far as your yield and maturity question, maturity time is based on the genetics of the strain and the environment in general. That basically means if the c02 has a positive effect whatsoever, it will increase the yield even if it's the smallest amount.
(at least this is what this noob has learned, I could be wrong!)