It used to be 6-9 months before people got scheduled for interviews at one point. For me it always helped having low expectation. When I filed N-400, I was ready to wait over 6 months (processing time was 7 months). But it was a nice surprise to get approved within 3.5 months.
There's many factors here: how busy the office is in your city, whether you have other pending cases (I-751), background, immigration history, and pure luck