I agree with 4U. It can be done at any time. I have seen a plant with 3 solid trunks coming out of the ground. It was topped at the second node and all 3 tops were tied to the ground about 6 inches from the trunk before it was allowed to grow. WIDEST plant I have ever seen outdoor (~10 feet wide, 7 foot tall).
Personally, I let the plants grow tall (2 foot), then strap them down. Each of my 4 plants lays on top of the next, in a square. Then I tie them into the middle to fill in. I tie them to the wall so they dont fall inward (it WILL happen to you when budding eventually) then use "yoyo's" to hang them from the roof.