Probably 20 years ago, they were raising the PP fee, doing the math, it was cheaper to renew 3 years early. I mailed my renewal appl. on a Saturday, I received my new PP on Thursday (5 days later)--this was done in Feb. or Mar. ("off season")...but NO expedited (anything), all by regular US Mail.
[I recollect the processing center was in Pittsburg.]