I'll put my two cents here.
With the new electronic Airman Application program where you complete your 8710 on a computer with your Examiner as you complete your check ride and electronically "mail" your paperwork to OK City you will have your certificate at your mailing address in just three weeks. So let’s review how it works other than electronically.
You take your check ride and pass. The Examiner puts your 8710 in his/her brief case and drives away. To save on postage they wait to get a couple of 8710's together to mail to the FSDO. (I knew of a flight school that waited until the stack was at least 3/4 of an inch thick before the mailed it. It took months to leave the school. The FSDO fixed that but every one still blamed the FAA)
Time frame: a couple days to several weeks.....
It takes the mail around a week to arrive at the FSDO.
The Inspector assigned to the flight school or Examiner has several stacks of 8710's to quality control check prior to sending them to OK City. If he/she isn't out doing check rides or ramp checks, or any other required work, they will be reviewed soon or in a while. Remember we schedule 60 to 90 days in advance because there can be many schools in an assigned region and they all want priority. With the staffing levels in the FAA we can have several jobs to do at once. This could take several days to several weeks.
It takes a week to mail to OK City.
The Regrestry in OK City processes millions of documents a year. Yours goes into the pile with all the other FAA regions flight schools and requests from airman. A document Examiner will process your application. They will go research (from a wall of micro-fish file cabinets) any document history to ensure you have the required certificates to obtain the next level. This is not on a computer data base. No money to update the system from the 1960's. On top of this Congress mandated that all Flight Attendants will immediately have a "certificate" for security reasons. No extra money or people were given to the FAA to do this. So this really slowed down the system.
Short answer:
Examiner - a couple days to one month (or more)
FSDO - a couple days to one month (or more)
OK City - One month before the Flight Attendant Certificate
One more thing, To process your application - Free. In other countries I have heard of a $100 (US) processing price tag. Think about that before you complain too loud. Can the process become faster? With the new computer system - three weeks at your door. I can't wait till this is out for everyone to use.....
I hope this is of some value to you.
JAFI