Originally Posted by KLouis

If you are not a US citizen, it may well mean another 120ish minutes. That's by experience! When coming to the US, I always plan an, overall, 3-4 hours long connection time (from arrival to departure, incl. terminal changes, etc.), although it's a fact that in 20% of the cases my stay at immigration was shorter than 15 minutes. Strangely, my shortest and one of my longest immigration clearance times (5 minutes and ~130 minutes, respectively) were both at ORD, arriving with TK at the same time of the day. My "negative" record was at MIA (a little longer than three hours) while in BOS I've never waited for longer than 30-40 minutes at immigration.

PS All of the above times were flying business class, i.e. being one of the first out of the plane.