It all depends on your service center and local office you filed. For example, if your filing in Dallas service center and your local office is in Rhode Island, it will only take a week for USCIS to schedule a date and time for your interview. Had you filed the same from NY, It would take almost 2 months to schedule for your interview. In my case It took exactly 40 days after the day i was placed in line for interview to  the day i was schedule for interview in Houston. So the bottom line is, it all depends where your local office is and how many filers are ahead of you. good luck.