There are two things at Abu Simbel that a day trip cannot give you.
The first is the Sound and Light Show. The temples are lit after dark and the story of Ramses II and Nefertari is told against the facade — and every day tour is three hours up the road by then.
The second is the morning. The site opens at six. The first road convoy from Aswan arrives around eight and the flight groups around seven, so if you are already in Abu Simbel you walk in at opening with the facade in low sun and very few people in front of it.
That is also the only time the light is any good; the colossi face east, and by mid-morning the whole thing has gone flat.
Staying the night gets you both, and takes the four o'clock alarm out of the trip entirely. You travel down from Aswan whenever suits you — morning or afternoon, from your hotel, your Nile cruise, or straight from the airport — check in, rest, and the day begins properly after dark.
Abu Simbel itself is a village of a few thousand people on the shore of Lake Nasser, thirty kilometers from the Sudanese border. There is very little to do after the show, which is rather the point. The night sky here is one of the best in Egypt.