It differs for everyone, but here is my hectic time frame
Started Hrt on June 13th of this year.
Told my best friends years ago. If memory serves 4 or 5 years back.
I told my mom 4 days ago. I was on hrt for a week.
I told one of my sisters the same day as my mom.
I told my other sister two days before starting hrt.
This is my list for now, besides support groups, online forums, and medical professionals. As I am still in the beginning of things, I have some more coming out to do in time. But I hope my short list was somewhat helpful.