doesn't matter. whatever you prefer bro..
you can start flowering any time you want to. hell, you can flower straight from seed if ya want.. but generally a plant that was flowered from seed will take longer to start actually flowering... then compared to a plant that's had two or three weeks or more of veg time.
Also, don't forget... flowering cannabis plants will at least DOUBLE in size.. sometimes even triple in size once flowering starts. So make sure you have adequate room for when it starts flowering.
good luck..
peace.