You can bend the plant at anytime you like.....the younger the easier it is on the plant.

Bending does not force the plant to do anything other than grow the main kola closer to the ground.

The objective to bending, assuming its not because of height issues, is to flood the secondary growth shoots with light...and....since those are where the bud stems come from, it reasons the extra light will foster larger bud shoots.

Bending is not really needed if lighting is adequate and getting to those secondaries to begin with.

Also, remember your initial secondaries will yeild tiny buds for the most part. It is the secondaries that are growing near the main top that you want to expose any extra light to.