when to put "under" vertical lighting?

I can't really find an answer. I have 5 plants under some t5's now, about six nodes...

When is a good time to put them in the vert room?
Should they be a certain height? Many horizontal grows, first vert. Seems considerably more efficient.

If you have the space, jus veg horizontally till they close to the height yu want, then flower vert. They wont stretch much upward once in flower.

Sir KK