Veg duration...

I'm taking away that around 16" to 18" above soil line is a nice height to switch.

If you want to maximise your yield then you switch when you have covered your lighting footprint with a 1ft thick canopy of green.

I like two gallon pots packed to 1/2 inch from the top with amended ocean forest. Veg 1 week in solo cups under 6500 k t-5's from germination to the 3rd set of leaves using a half dozen varieties of feminized indica strains and hybrids. Transplant and give them another two or three days of T-5 to recover. Sometimes i start the flowering cycle under the t-5's. I move my pick 6 to under my 400 watt HPS and flower using a ten hour light cycle. Each little pot produces a single cola with a few side nugs. I can harvest and sample 6 different strains in 8 to 10 weeks. I gradually reduce the light to 6 hours per day to get them to ripen faster. I get a variety of herb really quick at low maintenance and can test the strains to see which ones are keepers. Not to mention the little bonsai cannabis trees look cool as hell.