What controls when you have to respond to them is the law, not them. You'll know when that is, because it'll come with legal process.
One is none of their business the other is expected.
To give you some numbers: I operated an international community with about 1 million members over the course of 20 years. During that time the number of requests were larger than the number of requests that have been detailed here regarding Twitter, which is one of the reasons why I believe that we are seeing a highly colored picture.