Hi Jael,
I am assuming that you are not actually in Luxor as we speak, if you are this reply is a bit late. Also have you already spent some time there already? or will you be comming off a cruise or something like?
Luxor has loads of things for you to do that can take from several hours to a full day. here are some suggestions:
Visit the Luxor Museum of Ancient Art, good for 1 to 4 hours.
Visit the Mumification Museum good for 1 to 2 hours.
Go and have afternoon tea at the Old Winter Palace. say 2 hours
Have a look around Karnak Temple. 2 to 6 hours
Have a look around Luxor Temple, 1 to 2 hours
Get a taxi to Crocodile Island and have an ice cream at the Movenpick Hotel.
Go to any of the hotels and chill out for a couple of hours at the bar.
Cheap, good, safe food: Try, 7 Days 7 Ways up near the Sheraton Hotel.
Tez