Well I find that when I used CO² not only was my yield greater but the total time to finish was reduced by 2 weeks. You do need to have a proper sealed room and control the environment but YES it will reduce your over all time by 10-14 day's or more in some strains.

The only way to tell when you are done is by viewing the trichomes with a 30x pocket lighted microscope.

Plants don't read calendars; follow the trichomes to know for sure.
Zandor Reviewed by Zandor on . zandor and other veteran growers quick Q. does co2 speed up flowering time? this is first time ive ever used co2 and im at 54 days into flowering and they some seem ready. here's a few pics of my setup just to show you what ive been up to lately. Rating: 5