Hello, we are flying from Czech Republic to Sydney. We have 5h stop at Xi'an, (Xianyang Intl).

You cannot apply for the 72-hour free visa because you make two stops in China but the 72-hour free visa policy regulates that you can only have one stop in China.

But don't worry, you are eligible for the 24-hour free visa that it allows foreign tourists to have multiple stops in China as long as they leave the country within 24 hours. So if you make sure you can leave China less than 24 hours, you can qualify for 24-hour free visa.