Visa in Transit - clarification

Hello. I am a Canadian citizen studying in Hong Kong under a student visa. I am planning to go to Japan in March, and will fly through Shanghai. My layover in Shanghai is 20 hours so I was hoping to leave the airport and explore the city for the night. The rules above are somewhat unclear: Do I need a Chinese Visa if I am in China for less than 24 hours and leave the airport? If you could clarify that would be great!