Until plants cover wall to wall in space
When they flower they will stretch up not out. After stretch they stop growing up and produce buds.
Length of time depends on grow space and plant count, Pot size used, growth rate lots of variables. Starting in pots smaller than solos ending in 5 or 7 gallons normal veg for me is 2 1/2 to 3 months 4 plants in a 4x4
If you're growing in a open room your grow space is as large as your lights good for around the plant parameters
You can check out the 4x4 journal in my sig to see how 4 plants filled up a 4x4 when flipped at 5 and 7 weeks-both totally filled up the canopy. If you have a lot of small plants you should flip when they're much smaller, waiting even 4 weeks might be too much depending on your footprint. It also depends on if you are growing from seed or from clones because from seed, the plants need to hit sexual maturity before they start to flower-clones are sexually mature from the get go, so you can flip them at any size and they will flower.
Depends how you count it i suppose i give seedlings two weeks to be established before i count my veg time so proly 6 to 8 weeks in total lol never shorter than 4 weeks minimum unless its its something mental you got to grow on 12/12 from the start like equatorial kinda stuff id say