Visa validity length of stay

I want to apply for a 6 month double entry to China, but the second entry into China is on the 19th of June. I'm hoping to stay about 10 days in Guangzhou (so I would be leaving on the 29th). If I apply for a visa that expires on, say, the 20th of June, will I be able to stay for the full 10 days? That is to say, does the expiry of it affect the duration of your stay?