Flight Australia-Guangzhou-Beijing-Mongolia, 30 hours in China in total. Do I need visa?

I have booked a flight that departs Australia to Guangzhou, layover time in Guangzhiu is 6 hours. Then there is the second flight to Beijing. Layover in Beijing is 20.5 hours. After that my final destination is Mongolia. Overall time in China is 30 hours. However when I arrive to Beijing I can go to the passportr control and I can wait there until my flight to Mongolia departs. In this case I can put exit stamp from Chine within 24 hours. Can I do it as visa-free transit then? I have Austalian and Russian citizenship.