One month or more in veg, 8-12 weeks for flower, depending on the strain.
Early to mid January for a indica dominate, early to mid february for a sativa dom. (best case scenarios, full plant maturity)

Lowest temps without visible sign of stress is around 60 degrees. Below that and they seem to hibernate, so to speak. I've heard of CO2 in hot climates or enviornments, but not for cold. From what I understand, it's something about pore dialation and gas/air exchange in the stoma. (leaf pores that uptake air and emit O2 - Stoma - Wikipedia, the free encyclopedia)

If keeping it simple scares you, imagine losing a crop or two to jumping head-first into an advanced technique.

But, If you feel the need to spend the extra $ on an airtight/light tight enclosure plus the CO2 and monitoring equipment, and are familiar enough with indoor growing, it culd well be a benefit. But conversely, it can go bad just as quickly. The thread titled 3lbs in an enclosed growroom (or something like that) was dialed-in by an experienced indoor gardener, and his results are not typical to the novice. He is accostomed to his plants, his nutrients, his medium and techniques. He also is adept at troubleshooting, as the experience doesn't come overnight. I know you mentioned being experienced in outdoor growing, but you'll encounter a different set of problems.

Not necessarily trying to disuade you from the technique in general, but fantastic things can happen when you keep it simple. Less expense, less to go wrong, more peace of mind.

If having to build the enclosure just for the cold weather, there's no need for additional CO2 if you can vent-in some warm air or vent in fresh air, and heat the enclosure. Personally, I close my shed up at night and crank-up the heater. (away from the plants) No fresh air till I come in and open the vents in the morning, and the circulation fan(s) move the heat around. And there's no need for the heater during the day, as my 1000w HPS heats it just fine. Keep roots from getting too cold. (up off the floor)

Hope this helps, and I hope you'll have many sucesses to come. :thumbsup: