A classmate was awakened by the bell at night. He heard the clock striking, which was the last sound of 12 in the afternoon. Knock again half an hour later, that is, 12: 30 (once every half an hour), and knock again half an hour later, that is, midnight 1. Or 12: 30, wake up and hear 12: 30, then knock 1: 00, and then knock 1: 30.

Therefore, the student woke up at 12 or 12: 30 in the afternoon.