i think you mean sativa... salvia is that LOCO weed...:holysheep:
Plants usually become sexually mature at around a month or so of growth. Sativa dominant strains can triple or more while in flower so depending on how much growth it does in veg on 12/12 it would grow 3x or more. Many stretchy sat dom strains like Super Silver Haze are flowered immediately upon rooting or with only days in veg growth to end up with a plant that is around 3 feet or so... Indica dominant plants tend to double in size when flowered and I'm guess they would only get about 14" before flowering and end up around 30"... You would do better to veg the indica in long light imo but the sativa might do very well in 12/12 from the get go with the sativa genetics' origins being more equatorial.
The key with a main cola SOG grow is to flower them small before the side branches get a chance to develop. Some of this is strain dependent as well. Many growers remove all the shoots from the lower 1/3 or so of the plant because they will see little light. There's LOTS of SOG threads out there... Just Google 'SOG marijuana' and you get:
Paste this address into your browser and change the XX to tt...
I did salvia once myself, and all I remember is thinking 'this isn't working', and then waking up minutes later asking 'what happened'. Apparently I was laughing hysterically and trying to climb and invisible bookshelf talking about 'getting it while I can get it', so said my buddy guarding me who had himself done it before but I told him to watch me and not do it (spotting buddy). Longest 5 minutes of my life, and can't remember any of it.
LOL...I wish I could forget it. I watched my body shrink and my arms and legs grow very long, freinds in the room were laughing and I could hear them, but they were in a distant land....wierd!