So all my sisters know I plan to transition, and one good friend does as well. My mom died in 2002, so obviously I don't have to tell her. I had sort of planned not to tell any more family members until I was closer to HRT/surgery, because I thought it might be confusing for them to hear that I was now identifying as male when I was still largely presenting as female.
Then it occurred to me that it might actually be more traumatic for my dad to be told, "Hey Dad, I'm transgender. Getting the boobs lopped off tomorrow. See ya, bye!" Maybe a longer lead-up time would be kinder, since there would be more time to adjust and ask questions. The issue is that I suspect I won't get an ideal response from him. He's 70 years old, and I'm 44. He's pretty used to seeing me as his daughter. He knows I suffer from major depression, and he's going to assume this is part of that. (Which it is, sort of, but not the way he'll assume.) He may well decide that I'm nuts. He's not LGBT-phobic or anything, but attitudes can change when the "T" stops being a letter on the end of a weird acronym and becomes your firstborn child.
I'm interested in hearing from people who told potentially problematic relatives early on versus late. Did it go well? Do you regret not waiting longer?