In response to the OP, do you think the AA or US non-rev travel system doesn't have the capability to detect an "early" check-in? Not the post above that says someone who checked in 4 minutes before the 24-hour window opened got a warning email about it. Now, maybe 48-hour check-in was allowed in the past, and technically the QIK system still allows it. As a former IT person, here's why I think you are able to do it, and why it is not a good idea to try it.
1. The QIK system will probably go away at some point. (I was told that AA had a replacement for Sabre in the works several years ago. However, a system that big is not replaced overnight.)
2. The IT people decided not to modify the system to enforce 24-hour window because the cost to modify was greater than the benefit of blocking check-in prior to 24 hours.
3. Easier to write a small "oversight" program which would capture early check-ins and issue a warning.
Rather than test the system and risk losing your travel privileges (or, possibly your job), I would stick with 24-hour check-in. I know that the AA side of the house has always taken a dim view of people who attempt to circumvent the system.
Remember, on most mainframe computer platforms (the computer that Sabre runs on), there is an audit timestamp attached to every transaction...the date and the time the transaction ocurred, the location where it was entered (down to the actual terminal used) and, the id of the person entering the transaction (or rather the id of the person who is ostensibly logged on at the moment. This is why you don't give your id and password to someone else. If a "friend" uses your id and password to try something "illegal" on the computer, the computer is going to say you did it.). This is part of the basic operating system programming.
Oh, and I wouldn't be too overly confident about the agent on that earlier overbooked flight rolling your listing over to the next flight. I know most of them do that, but there are some who actually "work" the standby list and page people on the list to come to the podium where they tell you that the flight is full and you are being rolled over to the next flight. If they get a "No Answer" to their page, or you say you don't want to be rolled over (you were headed to a hub to connect to a one-a-day International flight and you don't want to be stuck at the connecting airport), your name will be removed from the standby list.
