Visiting the Graves of the Righteous

Shalom, I am secular, and I wanted to ask whether it is permitted to visit the graves of the righteous during the Three Weeks. In addition, I wanted to ask: I would like to visit Yonatan ben Uziel, and I understood that it is better to go at the beginning of the month. Is that true? And is it permitted to go on Tisha B'Av, because I know these are difficult days and I do not know whether there is a specific restriction. I would appreciate your answer as soon as possible!!!