Chinese Visa from Mongolia

Hi,
There seem to have been a few similar questions here. I am a British Citizen living in Australia. I leave Australia mid June and hope to go to China (from Mongolia) at the end of August. This is very close to the 3 month limit for entry and if i am delayed I will not arrive in time. Can this 3 month limit be extended? Also I dont have a flight yet as im not certain of my dates.
Thanks,
Alice