Upvote:4
You can apply for a visit visa immediately - and it doesn't matter whether you apply for B1 or B1/B2.
In practice, there's no reason not to go for B1/B2 - if you can convince the interviewing officer that you're a bona fide visitor, you'll get it. You may be issued a plain B1 visa depending on the circumstances, but like I said, no harm in applying for the combo visa.