I think the ones going straight into flower are the guys with aerocloners. Their roots are usually long enough to reach the bottom of the 2L.Most people running 2L bottles seem to go from rooted clone, right into flower as vegging it is a mute point since they are basically like GYRO is doing, and just growing ONE BIG BUD in each 2 Liter. From what I have seen, 2 liters are meant for SOG's, so no need to veg,, In fact most are Defoliating and letting the light get all up on the bud
Mine were taken kind of small so after they were transplanted, they were left to veg about 10 days. They were really starting to take off so I figured the roots had hit bottom or were close to it. Now that they are under the HPS they are growing like crazy. I already had to trim off the lower stuff. It it too early to defoliate, but they are touching. My scissors are ready....