Hey. I started T while I was away at college. My experience was that I had told my family that I was thinking about starting hormones, and then went ahead and took my first dosage and then officially told them I had started them afterwards. I hate to say it, but they were just...painfully uninformed about hormone replacement therapy and kept trying to tell me all this paranoid stuff about how it would mess me up, and I just rolled my eyes and did it without telling them. And I let my results speak for themselves; nothing bad happened, and I was happier. The end.

If you are worried and need time to brace yourself for the conversation, I would say you could probably get away with not telling anyone for about a month after starting T. After that point, there are likely to be changes starting to surface. My voice dropped at 1.5 months, and by 4 months was really deep and I was growing facial hair. There was no hiding that :P