When I asked AA how long a NY connection could be (LHR-JFK-GIG), they told me that they count anything over 23 hours 59 minutes as a stopover, which incurs an extra charge depending on the fare. I'd advise you to call the airline to doublecheck, but I'm sure you could persuade them that one minute (21:30 landing one day and 21:30 takeoff the next=24 hours unfortunately) between friends isn't a big deal. Then again, it might be a computer thing which a nice agent would have to manually override. I'd be curious to get their answer.