Best I can tell there is absolutely no link to the process; I have my interview coming up and the "months to completion" haven't changed other than by counting down by one every 30 days (showing 6 months right now).
Just received the interview date (September 21st in NYC).
Filed by mail, 5 year rule; received by NBC 7/1, Biometrics reuse 7/6 and now interview schedule, 8/5.
Your email might still hold them. If you have google maps on your phone, the location history can help a lot to figure out travel dates. USCIS/CBP will have your flight data, naturally.