A sentence refers to the pair of words which is complete in itself. In other words, a sentence contains a subject and a predicate or it may contain a main clause and one or more subordinate clauses to convey a command, exclamation, question or statement.
Subject refers to a thing or person which is being talked about, described or discussed.
Predicate refers to the part of a sentence which refers to the subject and contains a verb.
Hence, in the above sentence, the complete subject is - twelve hours
complete predicate is - passed without a word from any of the group.