So I know every strain is going to be a little different, but on average how long does it take from initiation of 12/12 light schedule to full bloom, more specifically how long does the stretch last? The reason I ask is I’m trying to keep a sativa short. I’m quad lining her and she’s just now starting to put out her branches.
You are spot on saying every strain is different. Actually every seed can be different.
As a rule of thumb, expect 
stretch to be nearly the plant’s height again from when flipped. 
Unless it is freakishly tall plant. 
@Tophat, I have found sativas often stretch close to 3x their height from first pistils to finish. I am not talking Sativa leaning hybrid, but Sativa. Landrace or Sativa crosses. When compared to hybrids.
I have found most indicas (not indica leaning hybrids) tend to stop, squat, and flower. The hybrids tend to be about the height they are (double) again at flower.
Totally generally speaking and could name outliers to my own statements.
I have found root binding in small 1 gallon or 1/2 gallon pots to be extremely beneficial in reigning in stretch monster sativas. Also topping one last time after initiation of flower phase. These are plants I ran more than once and proved to me they were stretch monsters.
They usually stretch for between 2 and 3 weeks when flipped to 12/12. I would expect it to at least double.
What strain are you growing?
100% Sativa or Sativa dominant.
Super silver haze, 90% sativa. I know I’m pushing the limits on keeping the beast under control. I guess what I’m really trying to find out is when in should I flip so it dosent outgrow my 2x2 tent. I’m thinking since I’m quadlining it as soon as I top the 4 branches I should flip. And then I will still have room to train them while they are in the early stages of stretching. That way some of the vertical growth gets trained horizontally and also keeps her short and fat.
Can veg her out. Train sideways or supercrop. I have had some sativa i had to crop twice.