How important is it that you take the later flight? If it is very important, just buy the one way ticket and have a confirmed seat now. DL isn't going to turn down additional revenue. If it is less important, either take the earlier flight or just wait until your departure date and try to SDC as other posters have recommended for $50 (or free if you are GM or PM) This only gets a little tricky if the later flight is the last one of the day. If you roll the dice, miss your confirmed earlier flight, and try to SDC and the later flight is the last flight and is full, then you are stuck in your departure city until the next day, with a very real possibility of having to purchase a Y fare (or have your ticket changed for a similar amount) to get you home. (of course many DL agents have a heart and possibly could accomodate you if the worst case scenario occured, but I try not to count on the generocity of others, even though I appreciate it when I find myself in these types of situations)