It depends on your field office. The extra wait can be as short as 4 weeks…and as long as, well, I have heard horror stories like 6 months…but ~3 months seems pretty common.
The officer was actually trying to gently sell me on just going for the Naturalisation since I could have had that the same day, downstairs. I said heck no, I have waited for 11 years, those measly 3 months ain’t gonna make me drop my new name! He laughed and understood, and 3 1-2 months of exact wait I got. Doesn’t even bother me. The deed is done. The stress is over.