I found this on Carnivals site so it may depend on what ship you're using
Frequently Asked Questions, Information | FAQs | Carnival Cruise Lines
Government regulations for U.S. departure ports require that a final departure manifest is submitted 60 minutes prior to departure. Guests must provide us with the required information prior to embarkation. The easiest and most convenient way is to complete our FunPass on line registration process (Embarkation Information | Carnival Cruise Lines
) at least (3) three days prior to departure. Guests that do not complete the registration process prior to embarkation are required to check-in at least 90 minutes prior to the published sailing time.
In addition, U.S. Customs and Border Protection will no longer be accepting oral declarations to satisfy the requirements for identity and citizenship documentation. Guests must present the proper travel documentation at embarkation. U.S. citizens traveling on other cruises (cruises that begin and end in different U.S. ports or begin and end in a foreign port) will require a valid passport or other recognized WHTI-compliant document. For complete information on the required travel documentation, please visit the U.S. Government website (Welcome to Travel.State.Gov