Wait... is JFK T8 TSA Wait Time that infamously bad? From my couple times stranded there having missed my DCA connection (BTW it's crazy after 8am the next AA flight is like 4pm), T8 feels essentially deserted in the mornings and early afternoons up to ~3pm when people arrive for transatlantic bank. AA has pretty much given up JFK domestic flights, and for the few flights that still exists they skew RJs and A321Ts where there aren't a lot of passengers.

Since CX831 departs around 250pm, probably people arrive around 1pm when the JAL flight would have all boarded. My guess is that the terminal will be mostly empty and TSA shouldn't be a huge problem at all. Plus the recent change that one no longer needs to remove shoes which also speeds things up.