Here's my experience... For benchmarking, I was naturalized on 5/29...
I tried to make an appointment online but couldn't, so I started calling. I tried multiple times calling my local office but the phone never got answered. In fact, if you hold too long, the system will just hang up on you.
Eventually, I tried the national number. Again, the hold time was very long. I tried on several different days and different times, but one day I got lucky and the call was answered inside 5 minutes. Ironically, the successful call was made around lunch time, which I thought would be a busy time. Anyway, the agent was friendly and confirmation was sent via text. The text had a link allowing you to modify the appointment. I tried the link a few times but it never worked. The only reason I tried the link was the text (there was no email) didn't contain the location of the appointment, only the date and time. I thought I'd check the location but never managed to. Anyway, not wanting to call again, I trusted the process.
The day prior to the appointment, another text arrived reminding me of the appointment. This text had another link, telling me to check in via the link when I get there.
Today (7/11) at 9am was the appointment. I arrived about 15 minutes prior, with a line welcoming me. I checked in and was given my ticket number via a confirmation text. The check-in link takes you to a web site, which has geo-fencing features on it, I guess to make sure you're actually at the office. Security came out a few minutes prior opening, reminding people not to bring any weapons in. Also, to not talk on the phone while inside in case people mentioned their SSNs. He said if he sees anyone on the phone, they'll be asked to step outside and potentially miss your ticket being call and have to start again. Then he asked for people wanting a SSN, we got pulled out of the line. He checked our appointments.
Sat down at the lobby. Another few minutes wait and I was called to a desk. A very kind lady asked how she could help. I told her I was recently naturalized and need to have my records updated. She congratulated me and I gave her the SS-5 form and my naturalization certificate, along with my DL. She pulled up my record and said, oh yes, it needs to be updated (so don't trust the n-400 form that it'll tell SSA to update). She checked the details, asked me my mother's name (I guess just as a verification measure), put my DL under the blue light to check its validity. Then she printed a receipt and asked me to confirm my name and address.
She said the new card will arrive inside 2 weeks, if not, call and reference the receipt.
Moment from parking the car to leaving the parking lot was about 30 minutes.