I haven't grown them in awhile, but I think I used to let them bloom and then pinch them back before they went to seed. Hopefully someone with more knowledge can give you a definitive answer.

Totally Confused

I pinch them before flowering. However, I don't grow Rockets, I don't like them as well as some of the other types. They need to be staked, and being the lazy gardener that I am, I prefer not to bother with it. I grow the medium height types, about 18" - 24" which not only do not need staking, but I find that when I pinch the main stems out, the plant branches out nicely and blooms better. I think the short and medium height types bloom more heavily than the taller kinds. My snaps keep flowering right up into the fall, as late as Nov. some years, and in zone 5, that can be pretty cold. Just keep deadheading them, don't let them go to seed and they'll keep blooming and blooming. Snaps are my favorite annual.

You accomplish the same thing as pinching them back when you take off the leader after it has flowered a bit. As long as you take it before it starts making lots of seeds on the bottom.

In all plants the top or leader is the prime seed maker and the branches are secondary. Most of the good goes to that leader to help it make seeds. When that top is pinched off without it making seeds then the plant goes into survival mode and the good goes to all it's branches are equally, and you get more branching and more flowers. That is why a plant bushes out after the top is removed.

With your rockets the plant is naturally slender, not bushy. That is why they're called rockets. I don't think pinching it back before they bloom is a good idea. It will never bush out like it's smaller cousins.

I never pinch back my little darling snaps and they are always bushy. In fact I never pinch anything back, but rely on removing the leader before it goes to seed