We were on an eleven day Horizon cruise in January and the menu did not repeat.
You can take it to the bank that you will be offered lobster tail, prime rib and baked Alaska at least once during your cruise.
I believe shrimp cocktail and Caesar salad are available every day.
On our last cruise, we relied on our waiter once we had narrowed down the menu choice. We were at the second seating. He always knew the better choice. In addition, he would always have a comment about , "Well, we are going to have shrimp cocktail on the menu again tomorrow night. Or, the beef is a bit overcooked tonight. He was a great help in picking great items and having a very varied menu during our a cruise. The downside was that he was very disappointed if you didn't follow his advise after requesting it.
Here is a website that has some typical Celebrity menus.
http://cruiseclues.com/
Enjoy!