My current grow is my first experience flowering plants indoors,so I'm not an expert,but
I can tell you what my plants have done since 12/12
I flipped them at day 35,they were 6" tall-remember,I used nodes 1 & 2 for the quad training,because I topped them about an hour before I found the Quadline thread,so they started out a few inches shorter than if I'd of done it the right way...
So today,20 days into 12/12,they're 15 & 16 inches tall,and I think they might be about done stretching-they've only grown about 1/4" since yesterday.
So,when you do flip yours,you can probably count on at least 9 or 10 inches of stretch.
Yours will be about 29 or 30 days old by the end of the week,which seems early,but with our space limitations,you probably can't wait much longer...
I'm guessing your plants are about 8" tall now(?) so if they stretch 10",you'll be at apx. 18"-and when they're done stretching,they continue to grow slowly as the buds stack up.
And they'll probably be an inch or more taller by the end of the week.
I don't remember how much headroom you've got in there,but I think your plan to flip them at the end of the week is a good one,and probably necessary so they don't outgrow their happy home...
And I want to add that I'm not sure mine are done stretching,but they've slowed way down,and I really hope they're about done...at this point the canopy is 12" from the lights.