I'm not really familiar with rules other than UA, where you can do SDC (Same Day Change) if same fare class is available and it's within 24 hours of departure. There is a detailed thread in the United forum for details. But unless you have Platinum or higher status, there is a $75 fee.

Of course this is most useful for EARLIER departures, BUT you can checkin (or not), and they go through steps for checking in online or at the airport, and if there is a later flight AND there is same class fare availability you can extend your stay. This would of course be most useful if there are plenty of connections, which does not really apply to too many int'l flights. OTOH, some flights don't always depart at the same time every day ... But unless there is a big difference in time, this could be a problem, because if it didn't work, you'd have to be at the airport so as not to miss your original flight if you couldn't do SDC.

You can also choose a connecting point where there is no daily service. IIRC GUM-HKG on UA is one such example.

A friend of mine also showed up at the airport unshaven and a bit smelly, and they asked him to kindly come back the next day, so he got his extra day, something that was denied over the phone.

I was in San Diego last week, and was offered Monday departure instead of Sunday, alas I had to be in work, so could not take advantage of it. I was also changing planes in DC, last year, and just for kicks went to boarding pass machine, and it offered me a couple of flights back to Dallas on a Sunday, so I could have had a domestic layover for free (on domestic connections anything over 4 hours or next connection is considered a layover).

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