PM sent.The amount of time is going to vary greatly, depending on what type of position it is, the hiring process that was used, the agency involved, and last but not least, the people doing the hiring. I know of one instance where the negotiations and actual job offer took place in less than a week, and another instance where it was drawn out over a month. Of course, the former was a GS-9/11, the latter was a GS-14.
Another item that’s often negotiated are the moving costs; this is why in recent years interviewers tend to favor applicants that live closer.