seats.aero has a Discord channel for paid members that shares new JL F availability in real time. Timing of F releases to/from JFK and DFW is all over the place. A seat can open up 4 days out, or 4 months out, or 11 months out. I am fairly sure that this is due to people canceling or changing award reservations and not due to JAL releasing extra seats, as there is no reliable schedule to it, and almost invariably there is only one F seat available on TPAC A350 flights (every now and then there are 2 on LHR or 3 on SIN).