I should have been clearer in my original post. These are two seperate tickets in question. I already have a ticket from ATL to BOS on DL departing at 2:30 on 10/10. I want to book an additional flight on DL to BOS, departing on 10/7 returning the morning of 10/10. I don't think this is back-to-back ticketing. Basically I want to go to BOS, come back, then go there again on the same day I get back from the first trip. Is there any problem with that?

I do have a couple other options. I could fly on US, but the times aren't significantly different from the above. Or, I could fly into ATL on the night of 10/9 instead of the morning of 10/10. I would rather not stay in ATL overnight, though.

As for the idea of flying on the 9:15 nonstop, I thought of that, but that is a K fare and raises the price of the ticket by nearly 40%. I don't have elite status on DL (yet) so flying on the K fare won't allow me to upgrade, either.

The "ghastly hour" flight leaves at 5:55 AM, and would probably mean having to leave for the airport via a cab around 4 AM. This is not very appealing...

Further advice would be very welcome!