How quickly can I have a visa to China?

Ni hao! I booked flights to China, Beijing (24.3 - 3.4. 2013). So I need a visa to China, but my problem is that before the trip I'm going to travel in northern Thailand and Laos. My plan was come back to Bangkok on 20th of March, can I get the visa in just 1 or 2 days? Or should I come bank earlier? I thing I need to get passport back latest on 22nd (before the weekend). BTW, I'm a Finnish girl and I'm studying in Bangkok.