Thanks for all the input. The tickets I purchased were 4 first class using Amex membership points so that should give me flight flexibility since (I assume) that they're unrestricted tickets. I looked at alternative flights to STT, such as United's non-stop from Houston, but that gets in pretty late (3:40) so catching a ferry is another issue. Flying to EIS jumps the fares way too much.
So based on everyone's advice I'm going to talk to Delta about moving the HOU - ATL and SAT - ATL legs to the day before.
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