Here is depends on who is doing the quilting. One gal has a 6 month wait list, yes 6 months. She does a lot of high end quilting. She is one the most expensive in our area.
Others are a little more resonable and turn around is normally around 4 weeks.
I would give her a date to have it done by and not just say, 4 weeks. That way she knows you need it by that time.