Overlanding trip in China

My son, 19yrs ole, is going to be travelling to China on an over landing truck (with Dragoman, the travelling company). He needs to apply for a visa for China - he is a South African citizen. How long does it allow him to stay there for as the trip is two and a half months long. He will also be visiting Cambodia and Thailand as part of the trip.
I look forward to your reply.
Thanks
Tanya