Depends on the time of day and how many people are on the plane with you.
My last trip from Australia, from landing in LA to going through customs and then going to terminal 3 and through security again took me just 2 1/2 hours. Customs actually went fairly quickly (about 45 minutes), but once I got to terminal 3 and had to go through security again, the line was down the escalator and out the door. That was the longest part. The time of day for me was around 11:00 am..........