Applied for FBR based on Irish born grandparents (used grandfather), both of whom were born in 1891 and emigrated to USA in 1911 (on the Lusitania...!!!)... Timeline was as follows:
Dec 2017 document gathering and application completed with photos and witness signatures
Jan 09 2018 completed and paid and documents mailed with receipt proof. Proof delivered Dublin Jan 12
April 24, FBR and documents returned with FBR dated April 10
My documentation was meticulous, I made sure I had everything and it all crosschecked and met all requirements, even included a note explaining why my grandfather and father had no middle name on their birth certificate and later have middle names on several documents. Only issue I could not explain (and was never questioned..) was my grandfather birthday was the 14th on his Irish birth certificate and the 15th on all USA documents...no clue why other than the USA naturalization people misunderstood his Irish accent in recording his birth day for USA citizenship though they got the month correct...
. I was never questioned by anyone nor did I ever receive any acknowledgements.
With the FBR I applied for my Irish passport and from start to finish that process took 5 weeks and 2 days.
So best of luck to all of you, I am still walking on air that I can retire this year and live in the EU and my only regret is that my grandparents, who were UK subjects when they left their homeland, and my father (born in USA in 1929), are no longer living and could not share in my Irish citizenship recognition.