Call Delta back and tell them that you would like to be reaccommodated on US Air (You can connect thru Philadelphia and arrive at 10 pm). If you want to stay on DL, I'm seeing 2 seats available on the 6:40 pm flight to ATL. You could also look at using Delta Express to get down to Florida and then fly over to Las Vegas. Finally, you could fly out of JFK, LGA, or EWR if you really want to get the dates/times as close as possible to your original itinerary. Good luck!
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