When Should I Start My CO2?

Hello My Friends. Please tell me when I should start my Co 2 in my grow room. I have 2 20lb bottles with the right feeding valves I just have heard 2 ways to do it. My Son (he grows in CA But outdoors) says he thinks I dont apply CO2 until I start my Flowering. Is this accurate or should I Go ahead and start when my babies are 8" or so (they are just sprouting now) I am grateful for any advice you may render.
Peace,
Jeff

You can enrich your air with CO2 any time. It will speed up growth.
I like CAP PPM4 Co2 controller. It connects to a tank that has an electric solenoid... this thing makes sure you always have the right amount of CO2 in the room.. it is the best.. actually, it is the cheapest; not he best.

Co2 is great for all the stages of the plant life, as long as the levels are where they should be. Which is no mre than 1500ppm, is what i hear for faster growth.

I am doing what you said and am trying to keep it at 1500PPM, Thank You Very Much for your help.
Sincerely
Jeff