I veg 24/0. When I switch to 12/12 I will see the first set of white hairs in 6-7 days. When I used to veg for 18/6, then switched to 12/12 it took between 10-20 days to see the first set of white hairs. I will always veg 24/0 now, seems the plants grow much faster and things happen much faster when you switch to 12/12.