Do they grow at the same rate in flower?

So Im trying to plan my growspace here.

Say a month in veg they have grown 10". Safe to say the stem could be 30" or more after 8-10 weeks of flowering if I start 12/12 now?

Plants in question:

they will continue to grow but not nearly as fast

Thanks! +rep

No way, they might make it to 20" max.
if you want them bigger you are going to need to veg longer.
Give it another week and see where there at then.
Depending on whether they are Sativa,
or Indica dominant they will grow different ways.
Sativa being taller and Indica more bushy.