I wouldn't even think about anything less than 2 hours without GE. Depending on when your flight gets to LAX you might end up in the late morning/early afternoon rush when the Immigration lines will be long and the backstage Customs will be backing things up a bit. Most of the time I've been out of TBIT within about 45 minutes, mostly waiting on the bags to come down the belt. If I'm lucky I've gotten out around a half an hour and my best has been 25 minutes to the curb. Of course I've been caught in a couple of epic meltdowns and only made my connecting flight on one of them when UA forgot to reprogram the 757s.