It normally takes around a week or so. I had mine renewed couple of months ago. Its usually easier and faster if there's someone who can take it to the embassy personally. Otherwise you can just mail it. When you mail your old passport, application for renewal and a check or money order, be sure to include a return envelope with signature confirmation, just so that it doesn't get lost in the postal system. Also, if you want the passport renewed urgently, you can call them up and let them know. They are usually pretty good about sending it back quickly.