Originally Posted by cmtlatitudes

The FAQ says the check-in date. But they're probably still ironing out the details of the decimation. (Note: Bolding is AA's as written, not mine.)

When will I receive the rewards?

Rewards typically post between 3-4 weeks after your stay is completed with the transaction date reflecting your check-in date. If booked through our partner, Booking.com, the rewards typically post within 4 – 6 weeks after your stay is completed.