Question

The graduation ceremony lasted only two hours.

Answer 1

It's the complete predicate.

Answer 2

The answer to your question would be that "lasted only two hours" is the predicate of the sentence.

The predicate of a sentence is the part that modifies the subject in some way. Since the subject is the person, thing, or place that the sentence is about, the predicate must contain a verb explaining what the subject does and can also include a modifier.