We are flying to Beijing and then Cambodia, returning from Vietnam on CSA with connection to Beijing

Arriving from US. We're staying at the airport overnight and can easily apply for the 24-hour direct transit. We fly to Siem Reap the next morning. Do we need a Cambodian entry permit to qualify for the Chinese transit G?

Departing from China. We will be flying from Ho Chi Minh City to Beijing on China Southern with one stop. Scheduled arrival in Beijing is 05:55 on January 19, departing for Washington Dulles at 12:30 on January 20. Will a 72-hour transit visa allow us to visit some of the special sites [e.g. Great Wall] during our brief stay?

Larry Wiseman