I didn't start using the men's room until I was a couple months post-T. I didn't pass at all, so I didn't feel safe. I know I would have gotten weird looks, so I just didn't do it. Most of the time, I just refused to use a public restroom. I was passing maybe 50/50 pre-T, and that's at best.
I guess I must have been three and a half-ish months on T when I started using the men's room. I was too concerned for my safety before that because I just wasn't passing enough. Now...I wouldn't even think twice going in there. Even though I don't STP, people don't care. I have a beard, a deep voice, there's nothing feminine about me... So it doesn't matter what I do, because they see me and know I'm a dude.