Can we apply the China visa in Sydeny without knowing the destination & actual travel dates ?

My husband and I had booked return tickets to HK from Sydney ( 19/11/15--30/11/15 ). We would like to make a short trip to China but haven't decided the actual destination.

We hold Australian passports. Will it be enough time if the back up plan is to apply the visa when we arrive in HK on 19/11/15
Thanks
Grace