Does the 30 days of a visa start at issue date or on arrival in China?

Our daughter who lives in USA is in the process of adopting two little orphan girls from China.. and we were going to meet her in Gangzhou and travel to pick up the little ones and then accompany them back to USA. When the adoption date is finalised she will have 30 days to go collect them and complete everything.. we have freelance travelled in China back in 1993..
We would like tohave all our travel doccuments arranged in advance... is this possible thrugh the New Zealand Chinese Embassy... thanking you Graham & Helen Dawson, Invercargill NZ