After the first interview, you are usually instructed to call them in 10 days to find out the result.
The time between first and second interview is anywhere from 6 weeks to 6 months depending on the circumstances. Average would be a couple months, but some people can't take the first interview available, or there are no more spots available so they get bumped to the next session.
In my experience, the second interview offer was the option of either 2 months or 3 months down the line.
Hope this helps.