I'm on AA136 next week, and in anticipation of that I just checked to see what the latest time would be to switch to LAX-ORD-LHR or LAX-JFK-LHR in order to get suites instead of coffins.

The last LAX-ORD flight that would connect to an ORD-LHR flight departs LAX at 330p (AA1546), and the last LAX-JFK flight that would connect to a JFK-LHR flight departs LAX at 215p (AA242).

I may be playing this game next week!