'Thirty' in the Bible

All the commissioners of the kingdom, the prefects and the satraps, the high officials and the governors have consulted together that the king should establish a statute and enforce an injunction that anyone who makes a petition to any god or man besides you, O king, for thirty days, shall be cast into the lions’ den.

Then they approached and spoke before the king about the king’s injunction, “Did you not sign an injunction that any man who makes a petition to any god or man besides you, O king, for thirty days, is to be cast into the lions’ den?” The king replied, “The statement is true, according to the law of the Medes and Persians, which may not be revoked.”