Moving to a later flight on the second segment?
 

Wife and I are meeting in ATL and ending up at the same final destination. She is going to be on the flight following me because of a significant fare difference.

Would the GA allow me to wait for her flight if there are seats available?

How far apart are the flights? One of you could maybe SDC to the other flight.

Do you have status? If you do not they will charge you 50 dollars if you have Gold status or higher you can do it for free.

As long as the second flight you want to change is a valid routing with your first flight, you should be able to SDC to your wife's later flight out of ATL within 3 hours of your first flight, so you won't even have to deal with a GA.

So if this fictional itinerary was for you + wife:

You
09:00AM AAA->ATL
12:00PM ATL->CCC

Wife
10:00AM BBB->ATL
04:00PM ATL->CCC

You should be able to call and SDC your second segment at 6AM.

the duration of the layover you are creating is also a potential issue. an SDC won't work if it creates a layover of more than 4 hours, at which point it becomes a stopover.

As mentioned above, this won't work because the layover will likely be too long, creating a stopover which is not permitted by SDC.

An hour. My layover in ATL would now be 2 hours instead of 1.

No I do not.

I stand corrected then.

If the new layover would become too long, you can try to SDC to a later first connecting flight also if it's available.

Actually it seems I stand corrected since the layover would only go from 1 to 2 hours. Both would be allowed. Since the OP doesn't have status it will cost some $$ but that doesn't make it impossible.

I will say that if your original layover at ATL is only 1 hour, there is a non-neglible chance that you'll miss your connection anyway, so you may get your wish granted for free :).

A little OT, but how long can a layover get before it is considered a stopover?

EDIT: Forget to read the above posts. question already answered