Having pizza available 24 hours means you can have it whenever you want on your cruise. Some times, such as lunch and afternoon hours, are the pizzeria's most popular time. If you want pizza for lunch or in the afternoon on a sea day, be prepared for a line, but in many cases the line will move fast. From my experience, most port of call days are less busy and a line can be short to non-existent. At night, the pizzeria is also popular. Many cruisers want a late night snack or something to eat after most dining areas are closed for the day. I have been to the pizzeria late at night and there was a line. Since the pizzeria is open 24 hours, this means you can have pizza for breakfast if that is what you want! I have seen cruisers eat pizza for breakfast, but I have not done this personally.
Over the course of the last several years, Carnival has been working to change it pizzeria style and menu. The vast majority of Carnival ships offer the following choices: Margheriti, Fungi, Pepperoni, Quattro Formaggi, and Proscuitto. This menu is much simpler than the old style menu. If your Carnival ship happens to have the old style menu, this menu will have a few more choices.
Can I get my pizza customized? While this is not a standard thing, there are some pizzeria crew members that will make custom orders. This depends on the person working the pizzeria. Personally, my special requests have been fulfilled at times, but at other times my requests have been denied.