When to apply?

I can't apply for a Visa yet because of the 3 months expiry date after you apply! But I'm not expected to Visit China until 1st July then make my way south to Singapore! However, im off to Australia first on the 13th April! Should I apply at the start of April in the UK and hope I get a visa through or apply when I'm in Australia for 2 months?! If so, how would I do this??