If a Firm wants to have further interviews with you, they'll probably call you in the next 48 hours or so, but the time could also be a week or longer. Depends on the Firm, but most seem to say the call will come sooner or later.
Then, you have a callback. YOu may go out to dinner the night before. You typically go to the Firm in the morning, and you'll meet with anywhere from 6-9 people or so, usually 20-30 min. interviews. Then you usually get taken out to lunch.
Not sure how long it might take to receive an offer after a callback. my first callback is this morning, so I haven't gotten there yet.
And if a Firm doesn't want you for a callback, they usually mail you a rejection letter.