Boarding at LAX typically starts about 45 minutes or so before departure, with preboarding for those who need assistance, and finishes around 15 minutes before departure, though of course all sorts of things can delay this. Formally you must be at the gate 20 minutes before departure and I'd advocate 30 minutes. There are 3 boarding points at LAX and it doesn't take much longer than any other wide body aircraft on the whole.

Hope that helps, don't hesitate to ask for more clarification.