How Much do Cheese and OG Kush Strech in First WK of 12/12

Like the title say im Growing Dinafem Cheese and Og Kush, ive been wondering how much do the strech in 12/12 since im doing Scrog and not sure if to fill the screen 70 % and switch to 12/12 , or Grow the screen 100 % in 18/6 and then switch to 12/12, i dont wante the Plants to Over grow the screen.

Thanks