Roz,
The only way that would be possible for crew rest purposes is if they were doing a high speed, stand-up, or continuous duty overnight. (they are called different things at different airlines) From some stuff I saw on other message boards, they say COMAIR does not do those on that specific city pair, LEX-ATL. I thought I had heard someone state they came in at 9:45pm last night. If that was the case and they could have been legal to show at 05:45am . Sometimes, due to van schedule etc, crews actually get to the airport before they are due and do their preflight stuff, but technically are not on duty until the 8 hours, that is why they could have still went on time, that is assuming rest was a factor.
From other reports I have seen, it does seem that they did take off from the wrong runway. Bill told me that it can be very confusing there how the runways/taxiways are setup, they have been doing construction there that is so recent the Jepp charts have not yet been updated, that combined with it being dark, possible fatigue etc. seems like a perfect setup for a disaster.
www.kentucky.com/mld/kentucky/15375985.htm
I hope the FO makes it through surgery. I also heard that an XJT pilot may have had family on the flight as well.