Originally Posted by Viajero
Up to 24 hours before departure, but it must be "same day", so, basically it means anytime after midnight on the day of departure. I have tried a few times to check-in the day before, without any luck, so it looks very much like a firm rule.
Yoiu can only check in at a kiosk 4 hours before a flight (domestic). Not sure on International, but I am sure it is not greater. Also I think the BOS Logan AA counter shuts down at 8pm (maybe it is 8:30pm now with the SNN flight leaving at 8:50PM). But I do not think the res system will allow to give you a bording pass the day before.