my 2 cents.
I really do not believe that you will see much difference to have C02 during veg. I believe that most growers never induce C02 until flowering, but I could be wrong.
On top of that plants indoors do not get big (1' to 2') until you are a few weeks into flower, unless you veg them for long periods of time. I believe they have ample amount of C02 during veg. I have seen studies on core samples of ice taken from the poles that were tested and show we have currently have 10x's more C02 in the atmosphere now than the planet has had in over 100,000 years of Earths history. Small plants are not going to be able to utilize all the C02 that is naturally around them, therefor IMO your just wasting your time and money by adding C02 during veg, unless like I said you have monster bushes I would just wait until you flower them.