'Thirty' in the Bible

It is common knowledge among all the king's servants and the people of every part of the kingdom, that if anyone, man or woman, comes to the king in his inner room without being sent for, there is only one law for him, that he is to be put to death; only those to whom the king's rod of gold is stretched out may keep their lives: but I have not been sent for to come before the king these thirty days.