Hi I need to apply for a visa via post, how long will this take as I plan on leaving on 5th May

I am leaving to go travelling on the 5th May to NZ and Aus but haven't yet applied for my Chinese passport for which I will be arriving there on the 1st July, how long will it take to gain a single entry 3 month visa via post as I don't live in London so not able to personally go to the embassy myself.