I grow fewer, larger plants and 6 weeks of veg is about my average. I have done as short as 4 weeks and done well though.
I count my time from when the sprout emerges and sets the cotyledon leaves.
Depends on what you want. They will double in size during flower. So just depends on space. If you don't have the room then flip it. If you do have more room leave it in veg. You end up with more yeild the longer its in veg