6 months passport validity from what date?

Hi, We are planning to go to China very soon. From what date is the 6 months validity calculated?

We are planning to go get the visa soon. At that time, I will have more than 6 months validity remaining on my passport. When we actually go to China for our visit, I will be entering with 5 months and 27 days of validity left. Will that be ok? So, is this 6 months validity a requirement of the day you apply, or for entering China?

Thanks,
Rich