Others definitely have more experience than me, but the amount of time you'll need is highly dependent on when you arrive, whether you have checked baggage, and whether you're a US citizen. My experience arriving on Saturday/Sunday afternoon has been that immigration and customs is very fast for US Citizens. My last arrival this past Sunday I was off the plane at 1:10 PM and past customs at 1:25 PM, with most of that time spent walking and 5 minutes spent waiting. But I think that's somewhat unusual, and I had only carry-on baggage, was in the second row of E+, and walked rather fast.

I've never connected at LAX since I live here, but if there is no special line for screening of international connecting passengers, security can take 30 minutes for elites - probably longer for non-elites. This is a worst case scenario for me though - typically elite wait times when I fly are 15 minutes, but I typically fly during off-peak times.

I would have a backup plan, because I personally think 90 minutes is very optimistic for an international connection and will require everything to work perfectly.