I mailed mine for renewal on November 4th to the Philadelphia office. I used Priority Mail, not for speed but to be able to track its delivery. It was picked up 11:30pm on November 5th. (Odd that they'd be working on a Sunday night.) The passport status website showed it as received on Tuesday the 6th.
It has already been mailed back to me and tracking shows it's due to arrive Monday, the 27th.
Total time, door to door: 23 days.
I did not pay extra for expedited service.
Right now is very off peak time for them and spring is the busiest. Just something to keep in mind. I considered waiting until January to mail it, simply to have a later expiration date. Our next travel isn't until mid March but I was afraid after the holidays it would take longer than usual. No one needs more stress in life, especially self-inflicted.