If ya gotta do it..ya gotta do it. Just be sure it's necessary. I convinced myself two grows back that one of my plants was root bound well into 12/12. It worked out ok I guess but it stopped the plant for a week and certainly lost yield and probably wasn't needed. You probably know this but you can check your roots by sliding the plant gently out of the pot and peeking. Why do you feel the need to do the deed?
You should already be in the final pot when you put her to flower. Reason is that when a plant gets transplanted to a bigger pot the first thing it does is grow roots
to fill the pot. You want that action to take place while she is still vegging. You will be wasting time waiting for the roots to grow out.
Yea I usually go one month in a solo cup. Then transplant to its final home. I give It one week to adjust. By week 6 thru possible 18 they go 12/12 and nutr slowly get leeched in gradually increasing strength as needed. I never liked transplating more then one time. Easier to avoid the extra trouble and work and risk of shocking your plant.