Vegetation to flowering?

I'd use some LST and could flip to flower any time. Would not wait much longer. Plant is a bit small for its age but its a good start.

Flip when you see fit you can still control the stretch by light hight or intensity or a late toppingvuf she grows to high.. Those leaves are droopy if she's not asking for water or lights have just come on there's another problem....

When it fills up roughly 1/2 of the area. You'll need to train it one way or another -- a scrog/trellis is definitely worth it. Always a good idea to work backward from a 'target canopy'. I want at least 3 colas per sq ft. So i know what each plant is responsible for and can form a plan to get there the most systematical way possible = less wasted time and resources. If your canopy fills the area and you have ~3 colas per sq ft, you're yield will push 'max' relative to your methods as well as reduce effort required to prun and trim the plant -- almost no work if you don't over-crowd a canopy. think ahead... plan ahead.

You can flip whenever you like now. 8-9 Weeks is more than enough for most unless you are going for some further training like suggested. Ps: Would add some P(hosporus) to your feed and watch to not overwater ( looking at those red stems...)