There's absolutely nothing wrong with folks having a "non-binary phase" before deciding they're just a trans woman/man. Sometimes identities do shift; that's something to celebrate!
But for god's sake that doesn't mean that every non-binary person is on that same trajectory. Do not imply to us that it's "just a matter of time" before we embrace the binary. It's patronising and invalidating.
There's enough pressure from cishet society to conform to the gender binary in order to be accepted. We don't need more of the same from our own community.
Non-binary people deserve a space to define and explore our own identities, play with presentations, in our own time and our own terms. Some binary trans folk, respectfully, need to learn to be more comfortable granting us that space, that autonomy.
Even those who had a "non-binary phase" themselves. Especially them, in fact. 🙃