According to the visa service that I use, a Chinese visa now valid for 6 months instead of 3 months -- that is, you need to enter China within 6 months of the visa having been issued, not within 3 months. (The amount of time you can stay in China depends on the type of visa that you get. I have no reason to believe that this has changed.)

(Not sure how long this has been going on, but I don't recall reading about it.)