I just transplanted mine after 4 weeks of flowering. Its okay just be gentle and make sure you dont mess with much of the roots. Here are my plants. They have adjusted well and doing better after the transplant.
You should be in your final pot right after you do any topping or FIM'ing about halfway thru veg cycle.
Every time you transplant the plant will spend most all it's energy growing roots to fill the pot. You want
that growth phase to occur during vegging.