Multiple entries into China with one day layover on one visit.

I am traveling from LAX through Guangzhou to Perth, Au with a 17 hour layover which plan on leaving the airport and exploring the city. Coming back from Perth I go through Guangzhou on my way to Vietnam but don't plan to leave the airport. Then again from Vietnam I go through Guangzhou again on my way back to LAX. This all happens within three weeks. What piece is well I need?