You will need to actually check-in on Friday or will lose your reservation. At least I've never heard of anyone paying for Friday and showing up a day late to check in. Many hotels do not accept Saturday arrivals. There are several that do though.

You may want to spend Saturday night at one place and then book the Luxor for Sunday night on. The dates you have chosen are such a slow time in Vegas that if you call the hotel they may be able to override their system to allow a Saturday night arrival.