i believe it is also better to tell them straight out, if you like them and/or suspect that things could develop into a relationship. it's hard to say what the other person would do but honestly that's my own policy, and for my own benefit. if you withhold it on purpose, you will be obsessing about it until "the big reveal," and also, you're intentionally hiding something which is misleading. it sucks that society in general is so damning toward trans and nonbinary folx, but honesty is still the best policy. you can't control the outcome, only your own actions.

the other thing is a question of your own well-being. the longer you wait to divulge, the more invested the other person becomes emotionally, and likely the more attached to the person you become. it's better to let these things develop in situations where both parties are aware of each other's identities and motives. she's not the only one who could be hurt by a delay in opening up; you could be too.

most trans folx divulge right away, or as soon as they suspect it could become serious, for their own safety. many attacks against trans and nonbinary folx happen when the non-trans person believes one thing and then finds out another once things heat up. transphobic attacks are never justified, but many trans folx consider it a safety measure to disclose early on, so that could be another factor. this admittedly is a bigger issue for trans women than trans men, but it is really an issue for anyone who is not cisgender.

hope that helps. best of luck.