Zhengzhou city

I hold a Australian passport, Aus citizen originally born in HK. wishing to travel to Zhengzhou City, Henan Province from Australia on the free transit visa to meet an old classmate for meal before flighting to third country. May I use the 24 hrs transit visa to this region of China if I have a departing ticket to Japan with confirmed seat ? Is it safe to do so and will Zhengzhou city allow 24 hrs transit visa ? Anything needs to bear in mind thank you very much