As long as you like. 旅行证 is like a passport. Did you hear anybody got kicked out of China because his Chinese passport expired? Read the Q/A section on this page: http://visa.ywpw.com/visatypes/visa_abc.html
【在 L*1 的大作中提到】 : As long as you like. 旅行证 is like a passport. Did you hear anybody got : kicked out of China because his Chinese passport expired? : Read the Q/A section on this page: : http://visa.ywpw.com/visatypes/visa_abc.html