The prepositional phrase 'at twelve o'clock' in the given sentence functions as an adverb, providing information about the time.
The sentence "I will be there at twelve o'clock" contains the prepositional phrase "at twelve o'clock," serving as an adverbial modifier. As per Chapter 12, Lesson 2, prepositional phrases frequently function as adverbials, imparting details about time, place, or manner. In this instance, the phrase functions as an adverb, specifically modifying the verb 'be' by providing temporal information—clarifying the time of the speaker's presence.
Prepositional phrases' versatility allows them to act as adverbials, adjectives, or components of noun phrases. However, in this context, the phrase distinctly plays an adverbial role, emphasizing the temporal aspect of the statement and exemplifying the diverse functions of prepositional phrases in enhancing sentence structure and meaning.