I beg to disagree with previous posts about the reason for the recommended early (3 hour prior) check-in at Dublin. IMHO, it is a left-over from the days of the "Celtic Tiger," when DUB was literally bursting at the seams. In those days it was not at all unknown for the airport to become thoroughly congested, with long delays, hence the need to allow for a wide time margin. Of course, the Celtic Tiger has since joined the choir invisible, DUB is much less busy, and Pier D has opened, so less of a problem. So, my take is that AA have simply failed to update their recommended check-in times to reflect this new reality.