it depends
on things like class of service, terminal, etc. The last three times I've flown into LAX with checked luggage I went from seat to curb in under 20 minutes. The officers were courteous and professional, my luggage was on the carousel by the time I got there, and there were no lines anywhere longer than a few people. Granted this was T5 (Delta) and not Bradley (and I was in AF Biz), but even at the international terminal, I've never had to wait more than 15 minutes in the immigration line as an American citizen.
My worst experience by far was at Atlanta--immigration lines were OK but baggage claim was horendously slow, rechecking luggage took a long time and then the line to reclear security to get out of the international arrivals area and into the terminal took over half an hour.