Well you can switch to 12/12 any time you want. The longer you veg the bigger your plant will be. Plants double in size after switching to 12/12.

The plants look good but like they look to be streaching. Put your light closer to them. It looks like a MH glow..you can go pretty close w/ a MH depending on watts. .

As far as the brown tips and drying..there are many things that can cause that. My guess would be mag. diffeciency. That always starts in the tips.