I can't speak for Delta, but on American they do this when there's a schedule change. Perhaps your flight from JFK to Dakar was changed. It looks like it's only flying 4x per week. Normally they would contact you and work out a new schedule when there are major changes, but perhaps Continental didn't pass along good contact info for you when they booked the flight. I would call Delta directly. If there's that much of a schedule change, they should work with you to find better connections. Good luck!