When and how do BB's contact you for second round?

i had a phone interview with citi, not for ibd, and was emailed late the following day by the recruiter. -if this helps

It totally differs then. I interviewed on campus and was called a few days later by HR with an invite to the second round. Still haven't emailed with them once. I'd just shoot them an email to follow up if you need a decision quickly.

You can wait a week and still get a positive result.

during superdays in the fall they were calling back the same day .. but that was after an onsite interview when recruiting was really on their minds. Even when making offers, they would decide by day's end which was really nice

It varies, there's no "standard" notification procedures. That said, in my experience most of the time I was notified either later that day or the next business day. I've also interviewed at a BB where it took them almost a month to get back to me and the result was still positive. I should note though that these were all for SA positions.

usually after a week via phone