How soon can I apply for a B1 visa after returning from a J1?

There’s a two-year restriction on J1 visas which requires you to return to your home country and forbids you from applying for an immigrant visa. A B1 visa is a non-immigrant visa and so doesn’t count.

As long as you have indeed returned to your home country and that you can satisfy the inspecting officer that you are not using the B visa to circumvent the home presence rule or to try to immigrate, you should be ok. But you should be prepared to answer these concerns in your interview. Having a solid, steady job in your home country that you would return to would be a good way to assuage these concerns.

Yes, There is no time frame as such which stops you from applying B1. All you have to be prepared to answer queries regarding your previous stay and valid reason to have B1 now.