Top Law Schools

Is there an unwritten rule that all schools send out decisions before April 15 if the applicant applied before the school's application deadline? I don't know if I need to start making a decision among the schools I have been accepted to when I haven't heard back from my top choice yet.

No. NYU, for example, cites "late April" as its response deadline. Each school will vary, though, and you should check with them individually.