美国24小时的法律只管从美国起飞降落的机票。

Google keyword "air china 24 hour cancellation"

想当然了吧。请看air china的细节。东京到上海的机票不受美国规则管辖。

https://www.airchina.us/US/GB/faq/

In accordance with U.S. regulations, tickets purchased on Air China's U.S. website may be cancelled within 24 hours of purchase if the reservation is made more than seven days in advance of departure, and the ticket must include transportation from/to the U.S. To cancel a ticket, submit a cancellation request on Air China's U.S. website, and then call Air China's U.S. hotline on [phone].