If I were you, I would stay with the updated time of 6:50pm. Spend a few more hours in cairo would not be a bad thing, besides you can do late checkout, not a bad thing at all. Forget about the early morning flight, it got to be a torture. My situation is different, my inbound flight to CAI arrives in the mid of the night, and I need to fly to ABS the same day anyway. And you can do felucca after your Abu simbel trip next day. Or you can still visit museums instead if it's that important to you.
I just checked, a lot of flights in early November are sold out, and see some fare hikes as well.