Hi I am flying LAX-JFK-LHR-IST with the LHR-IST on BA metal. When I check in online for the AA portion 24 hours in advance it will be over 24 hours on the BA sector of the flight. Will it let me select my seat for the BA flight when I check in for my AA flight because BA doesn't pre-assign seats. So can I pick my seats 24 hours from my departure time of LAX or 24 hours from the LHR departure time?