when they are long enough to make a difference, you know with a big flowering plant one inch isnt much space, so i would way until theyre about 4 or 5 inches long so when i bend them they get away from the center, plus if you already have several nodes when you bend they will turn into stems growing up too, also consider that the plant branches will naturally tend to grow apart, meaning two branches close together dont always need you to tie down, give the plant some time to see the shape it grows into and intervene when the branches grow too tall to maintain an even canopy