Originally Posted by
Kid Flyer
what you can do is to buy a flex ticket and you can select a later flight online if you see that you will not make it.
...assuming that the later flight has availability (if s/he wants to do a same day change; otherwise a fare delta will likely be due even on a flex ticket) and the OP has internet access while being on the delayed flight. same day changes on a flex ticket can only be done on the day of departure (at least that's what I have observed / experienced) so trying to change a flight before leaving the US on the previous day is likely to be treated as a rebooking and not as a free same day change.