chasv77answered grow question 5 years ago IMO, all photoperiods can grow forever in veg state. Since quantity is always at the forefront, efficient usage of your grow height would be paramount.
My rule of thumb, not knowing a strain's characteristics, phenome, etc., would be to allow for 100-150% flower stretch, after the lights get flipped.
So whatever recomm distance of lights from canopy, you can calculate how tall your plant can get in veg.