Return from Shanghai to Toronto

Hello,

I am planning to book a flight from Toronto to Hong Kong and then Shanghai back to Toronto. I am visiting other Asian countries in between that time frame. I am flying to Shanghai from Japan on a separate airline carrier and plan to stay in shanghai for a day or two. Is that allowed? Or does my return flight have to be a direct "layover into shanghai" to be able to take advantage of 72 hour visa free transit? Please let me know!

Thanks,

Lily