10 hours could be the magic number then. On one flight I had more than 12 but on the other, I had a little over 8. So 10 sounds reasonable. I know there's a cutoff, but I don't know the exact number. AA wasn't a huge help when I asked this question either. The reservations agents had no clue about the rule and told me just to carry on a change of clothes just in case. I did pack a carryon but at the airport, they told me I had to reclaim because of the time I was in SFO.

Wouldn't it be nice if such rules were published so no guesswork would be involved?