It's whatever people write. There aren't rules aside from the ones stated in the first chapter. You're not going to have every story consistent on whether you can reinterpret the wish to have a time limit for the same reason that you won't have every story consistent on how many siblings Jon has or where his school is located. It's not written, so it's available for people to write whatever they want.
Also, even the rules in the initial chapter are somewhat vague. Remember that they were written by Jon's grandfather, who is still a human being. Is it really obvious that he's going to be so literal that when he says "earshot" it is meant to include sleeping people. Would you write that way? Maybe. Would every person in the world write that way? I doubt it.
That being said, it's certainly true that many of the stories have wishers who can't see obvious ways to reverse a wish, don't experiment or make wishes for information in order to find the exact limits of the stone, and are in general stupid. (It is more plausible somewhat because the main story deals with high school students.) You'd really think someone would read the Magic Stone List.
