Here is our timeline for embassy processing the PGR request (in case when when PA is outside of Mexico). All this is coming from GCMS:
We sent fingerprints and photos to Mexico and they were delivered to the embassy on Dec 11 2016.
On Dec 16 embassy forwarded the docs to PGR.
PGR issued the certificate on Dec 29.
On Jan 26 certificate was added to the file in GCMS, (I suppose after being verified/translated) and on Jan 31 VO lead officer confirmed all certs in order.
So overall about 50 days.
We also requested an official letter to take to PGR - this would probably be a slightly faster option through a carta de poder, but the official request letter took 2 weeks to receive from embassy, by that time we gave up waiting for it and just sent the fingerprints to the embassy instead.